If you want to "mix" two user files together - you've got to use the Library area as a temporary holding space for one of the two user files.

You cannot selectively load Performances from a user file. You cannot non-destructively load user files.

The only way to move a batch of Performances from one memory location to the user area without affecting existing Performances is to use Library Import.

As a preparatory step in any of this, I would first do a full backup of the instrument before doing anything so that if something was done in error, I could restore the instrument back to where it started before making attempts.

After backup, I would first load one of the two user files into a Library slot. Then load the other user file into the user area which will clear out all of the user Performances that were there previously. Then I would use Library Import and select some (or all) of the Performances in the Library Slot I used as a holding space. Now the user area will be a mix of the two user files.

How to add one or two performance and keep ( preserve) old user performances , that I created in user bank ?
If I load new modxNew.X8U than I delete the old. But I want both my old performances ( modxOld.X8U ) and modxNew.X8U together.
The last file delets the previous one.
Could you help me? Thank you.
Petr

Hi Petr,
There are a couple of ways to combine Performances. As you have discovered (and you receive a warning each time you Load a .X8U file) the act of loading a User File will replace all data in the current User Bank.

A User Bank can be ‘saved as...’ a Library. This File Type converts the data and when loaded writes it into Flash memory... You can load this Library temporarily, and then select which Performances you want... data imported from a Library can be added to the current User Bank without overwriting — it is simply added to the lowest numbered empty location. “Library Import” is how you can combine Performances, Waveforms and Arpeggios from various files into the current User Bank.
Link: __ Mastering MONTAGE/MODX User and Library Files

Alternate Methods
We recommend that when you take the time to create your own Performance data, you not only make a .X8U file, but also use the “MODX CONNECT” software or the “Soundmondo” Application to capture each individual program. This allows you to quickly assemble your own data into the User Bank. Both programs capture a Bulk Dump of the Performance which allows you to restore your Performances via a USB connection. This will work for Performance data only, it will not restore any custom Waveforms, Arpeggios or User Motion Seq Curves... but is ideal for Performances that utilize the 6,347 Factory Waveforms, 10,231 factory Arpeggios, and factory Preset Motion Sequences. It’s quick and easy.

If you have invested in the John Melas MONTAGE/MODX Complete Tools and the Waveform Editor, you have another way to assemble your .X8U Performance data into the one User Bank. This third party computer based suite of Editors allows you to assemble your data by importing your .X8U data directly from your USB stick. You can work entirely offline (in the computer), simply drag and drop the Performances you want into a new User Bank template... it then let’s you save as a new .X8U file which you can load to your MODX. This takes care of all User data including the Performances, Waveforms, Arpeggios, and Curves. These Editors are both quick and elegant. Highly recommended for those who want to take advantage of all the MONTAGE and MODX have to offer.

John Melas Site

You write :
To create a LIBRARY you must assemble what you wish to place in that Library into your USER area. From the USER area you can SAVE as a "Library File" - this creates a .X7L (MONTAGE) file, .X8L (MODX) file on your USB stick.

But how ? When I save user file I get automaticaly file with suffix X8U . Should I simply overwrite suffix X8U to X8L in computer ?

But how ? When I save user file I get automaticaly file with suffix X8U . Should I simply overwrite suffix X8U to X8L in computer ?

No.

You have data currently in your USER Bank... lets call it “Perf Bank 1”
Press [UTILITY]
Touch “Contents” > “Store/Save”
Set the “Content Type” = LIBRARY FILE
Tap the box that says “Save As New File”
Name the File “Perf Bank 1”
Tap “Done”

This will create a .X8L File from called “Perf Bank 1.X8L” we’ll refer to this as temporary Library - it will contain the data currently in your USER Bank

Next, LOAD this Library File — it will occupy one of the 8 Library locations in the Flash ROM area.
Now Load the other .X8U file that you want to expand, we’ll refer to this data “Perf Bank 2”

It will overwrite the current internal User Bank (as you know).
Now, using “Library Import” you can move Performances from that ROM Library and ‘import’ them (add them to the data in the User Bank... rather than overwriting, data imported from a Library simply is added to the data currently in the User Bank.

Go to the [UTILITY] > “Contents” > “Library Import” > select “Perf Bank 1”
*select* (place a check mark next to) each Performance you wish to add to the current User Bank area or simply tap “Select All” (if you want to combine them All)

This will instruct the system to ADD these selections to the current User area... thus combining data from “Perf Bank 1” with your currently loaded “Perf Bank 2” data... thus when finished importing, your current User area will contain “Perf Bank 2” and the items you selected to import from the “Perf Bank 1” ROM Library.

Once you have assembled all the Performances in your User Bank, you can DELETE the temporary LIBRARY

I recommend you Save your newly combined User Bank data as both a USER FILE (.X8U) and as a LIBRARY FILE (.X8L)
Keep a copy of these Files on your computer...

Hope that helps.

Extra Credit:
The reason it works this way is so that all functions that make your Performances sound properly must be cataloged — this includes not just the hundreds and hundreds of Performance parameters, but any User/Custom Waveforms, User Arpeggios, etc., are also placed in locations so that your Performance will sound properly when recalled.

As you have observed loading one User Bank overwrites completely the current User Bank. If your current User Bank includes your own or purchased Waveforms (new Samples), or if you’ve created your own Arpeggios, you want them to be placed so that when you recall a Performance to play it, the right Waveform, the right Arpeggio, etc data is also recalled. This Library shuffle ensures that the system “know” where to look to get that data.

Remember, many Performances can make use of the same Waveform data, many Performances can use the the same Arpeggio Phrase. So to avoid having to duplicate Waveform data and Arpeggio data, the system creates a new catalog that efficiently allows your Performances to find what it needs... when we say it “builds a new catalog“, we mean that literally, it places the custom data in the lowest numbered empty location, and then updates each ‘Imported’ Performance so that it know *where* to find what it needs.