Hi Dario,
Thanks for the question.

Scenes are now a combination of data links, synth/mix settings and can include looping Pattern sequence data. The two things can be dealt with separately.

For example, a Scene can be a link to a particular Arp Type and Motion Sequence, it can memorize Super Knob position, it can memorize your Mixing settings (Volume, Effect Sends, Pan position, Filter offsets, Mute status), Amplitude EG offsets, KBD CTRL status, and Play FX that apply ‘feel’ to Arps and Motion Sequences)... and new with MODX version 2.00, you can now store a Pattern Sequence with each Scene (1-256 measures)

If the Scene is without a Pattern, you can COPY any Scene by first recalling it by pressing its corresponding red button; then hold [SHIFT] + [SCENE X] (where X is he target Scene where you wish to place the COPY.

If, however, the Scene additionally contains MIDI Pattern data (a sequence) you would use the “Play/Rec” > “Pattern” > “Edit/Job” functions to COPY the data from one Scene to another. It is likely that this is what you are referring to.

Touch the “Edit/Job” box > tap “Track” > “Copy”
Here you can set the Track = All and the source Scene number, then below that set the target Scene. This will copy the MIDI event data recorded to the Pattern Scene. If you wish to apply the other settings - they will follow (persist) but are not ‘stored’ until you register them on the “Scene” Memory screen. If you wish to *lock in* the same mix and offset settings, also execute the [SHIFT] + [SCENE] routine.

While in the “Edit/Job” you will see the “Clear“ as one of the “Track” jobs... you can clear a single a Track or all Tracks in any Scene.

Extra Credit:
Please this article on Scene Memory: This applies to both MONTAGE 3.00 and MODX 2.00
The Power of the Scene Memory

It works, great! in my case I needed the first solution you described to me

now I have another question :

in my Performance I have the Main Effect --> Variation assigned to a Delay LR effect, it's not assigned to a single Part of the performance
I want to assign the " Feedback" parameter of this delay to the AsgnSw 1 Switch
in detail I need to have AsgnSw 1 Off = no Feedback delay / AsgnSw 1 On = yes Feedback delay at its maximum value of 63
If possible with a smooth transition between the 2 states : Off/On

I've tried everything but I'm not able to achieve it

You cannot assign the Assign Switches to control a Common parameters (Reverb and Variation blocks are System Effects and thus are on the Common/Audio level of the architecture).
The Assign Switches are available for Part control assignments.

Controlling upper level parameters like the Master Effect, the Reverb and/or Variation Effects is done with the following Controls: Super Knob, one of its eight Common Assign Knobs, a Motion Sequencer Lane, or the Envelope Follower.

Options:
_You can assign the Delay as an Insertion Effect to a Part, Parts can use the AsSwitches
_You can leave it as a System Effect and Control the individual Parts that feed it. (recommended)

It is not clear (to me) what you really want to accomplish. Here’s why: “Feedback Level” is the parameter that controls the number of repeats...even when set to +0 you will still get a delayed repeat, it is not the same as being Off (by any stretch of the imagination), it is going to give you at least one repeat... while the maximum offset would repeat forever.

If you hadn’t used the term “On/Off” I would not be (as) confused about what you want to accomplish. If you want to eliminate the delay entirely as one of the two conditions, then “Feedback Level” is a bad choice — as mentioned it controls how many repeats... but minimum is actual not equivalent to Off.

What is most important to you:
Using the AsSw?
Controlling Feedback amount (?)
Turning the Delay On/Off?

But as it stands, I’m not exactly sure I know what you want to accomplish. What follows is...

My best guess...
If you want a situation where you hear delay and then a second condition where there is no delay, this is best accomplished by assigning the AsSw1 button to control the Send amount to that Effect for the Part, or multiple Parts you are sending to that Variation Effect. This will give you a situation where when the
AsSw1 Off = no delay
AsSw1 On = delay

Here’s how to do that...
We assume you have the Varition Effect set to “DelayLR”
From the HOME screen, touch “Mixing”
Here you can see the MODX mixer
Select the first Part you want to control by tapping its “Var” Send control
If Off is one of the conditions you desire set the Var value =0
The [CONTROL ASSIGN] will glow indicating this is an assignable parameter
Press [CONTROL ASSIGN]
You will be asked to engage the physical controller you wish to use, press the [AsSw1]

You are taken to the Part Edit, ControlAssign screen where Assign Switch 1 assignments are shown
Set the “Curve“ = Standard
Set the “Polarity“ = Uni
Set the “Ratio” = to a positive value (+) start with +1, increase to taste... do not just set it to +63, instead slowly increase it until you get the balance of original sound to repeats that makes sense. It will be less than you think. Ratio here is the Send amount.

Let us know...

Note that if you really did want to have an assignable switch change common (upper) level parameters - you can still do this indirectly. I would add a part for the sole function of creating an envelope for the common level to follow. I'd use FM-X so I could set the an infinite release. When I strike a key - the sound starts. Moving to different notes wouldn't change the volume. And letting go - the volume would remain constant. I'd make it mono - so if I hold down many keys - the sound doesn't get any louder. I'd change the frequency to fixed so that any key will play the same note - to help keep the volume constant. I'd have no effects turned on (system or insertion) for this PART. I'd route the output to OFF (instead of Main L&R or otherwise) so that it's only used for generating the envelope and not heard.

Once that's setup - I could assign, for that FM-X drone PART - that the assignable switch forces the volume to silent. And pressing the switch again will bring back the full volume.

Once this is all settled - then envelope follower for this PART. Say this FM-X drone PART is PART #7: then Envelope Follower 7 can be used as the source and any of the system effect parameters available can be destinations. Pressing the Assignable Switch will indirectly modulate the parameter set as destination in the common level of the matrix.

My main use of envelope follower is to serve as a bridge between two "islands" that normally cannot relate without envelope follower as the go-between.

Ok, actually I've expressed myself badly and I haven't made the idea of ​​what I want to achieve more precisely. So I will try to explain things more clearly:

1) I have a Performance made only by a simple acoustic piano sound and it is only 1 Part, not many Parts. Here I've assigned the Delay LR as System Effect, so not as an Insertion Effect

2) I've assigned 2 Scenes to this Part:
Scene 1> Mixing 1 = Var Send 0
Scene 2> Mixing 1 = Var Send 127
in this way I can use the MODX as a looper for the same sound going from Scene 1 to 2 and vice versa, also creating overdubs

Now, at this point having said that, about what is most important to me, or at least what I have in mind to achieve is this:
Use the AsSw1 to Controlling Feedback amount from 0 to 63 (the max value)
That's all

Anticipating your answer, I believe this is not possible, right? This is because I'm using the System Effect and not the Insertion Effect, right?

Anyway, I've given a try to your last suggestion and the problem that I keep having is that the Delay L / R now behaves On / Off by responding to AsSw1, it's ok
but the Feedback (set to 63) continues in the background without ever stopping, although I deactivated the Delay with the AsSW1 key