You can edit the velocity settings to make it difficult/impossible to produce the velocity to engage the grace note - or you can edit the velocity parameters to remove this range which produces the grace note.

Examples:

PART 1 - Touchscreen: "Part Settings" -> "General" change velocity depth to 60 (edit: as high as "62" seems to work as well). I can no longer get the grace note to sound. The downside is you limit the dynamic range somewhat - but does work.

Or you could go to Element 3 and adjust the velocity range high end to 127 and turn element 4 off.

Really there's hardly any difference in the sound of the two options. One is easier to do (the 1st).

... as a side note: I do not see element velocity depth as a destination for Mod/Control. It would be "nice" if you could assign this as an output then use [ASSIGN 1] (for example) to change the velocity depth so when latched ON - you could use this method to control if the slide happens. You can still use XA control to do this sort of thing using the same button - but there's a reasonable argument to expanding the destinations to include more parameters. Maybe in the next generation.

Fingered Steel
This Steel Guitar instrument is built from 13 Elements across two Montage Parts. The basic core construction of this instrument features a four-way velocity switch version of the guitar played with fingers (thus the name) and a four-way velocity version in Part 2 that is played with a pick.

The Fingered (4-way) switches between a soft, a medium, and a hard fingered open string and a pitch slide set of samples (Waveform) and you can switch (using [AsSw2]) to a four way Picked version of this Steel string that switches between soft mute, medium soft, medium loud and loud picked Open string sets of samples (Waveforms).

A Waveform is a collection of samples (as few as 1 and a maximum of 256), that reproduce an entire instrument or a building block (Element) to build an instrument. There are a complete set of soft plucked note samples throughout the range of the guitar, a complete set of medium plucked note samples, and a complete set of hard plucked note samples in Part 1; at high velocity a full set of the pitch slide samples. A similar thing in Part 2 with the softest Picked set is a "Mute" string tone.

The other 5 Elements are used to enhance the array of articulations, sound effects and inflections you can produce when performing this fingered/picked Steel string guitar emulation... including the pitch slide, dead notes, finger noise FX, harmonics. As you play harder and faster you will hear your virtual fingers as they zing along the guitar strings (Key-Off)

You can watch a video tutorial where Tony Escueta shows how you can adjust the harmonics and other guitar articulations so you can "perform" a guitar on Montage... while not this particular guitar, it will certainly give you ideas about what you can accomplish... It's all about how / when you want to bring in the supporting Elements.
https://youtu.be/tBGx6xcq6dg

The three principal (Fingered) Open string Elements are supported by the other Elements to create a perform-able Steel string guitar instrument with lots of nuance and inflection:

If you don't want to use the pitch "Slide", with the above overview of your Elements you can see that PART 1, Element 4 (which you identified as the pitch Slide) takes place only when the velocity exceeds 124 thru to 127.

You can simply turn this Element (4) OFF and increase the Velocity Range of the "Steel3 Finger Open f" located in Element 3, from its stored setting of 106-123, to cover the space vacated by the "Steel3 Finger Slide": 106-127
The edited version would look like this:

Do not worry about creating a hole, if it is not an Articulation you desire, program it away. It's a synth.
Try the [AUDITION]
Let it play through normal, second play through press and hold the AsSw2 button... this will now let you hear the Guitar played with the PICK. Release [AsSw2] to return to the FINGERED played. The switch is set to momentary (your choice) so the performer can switch between a more focused tone (pick) and the more rounded tone (fingered) as you play.

Below is a view of the XA Control, Note and Velocity mapping of Part 2 (Picked) 5 active Elements... includes the harmonic [AsSw1]

Jason / BM — I dedicated some study time this afternoon to review your comprehensive tutorial on this. I can follow the theory and how the velocity limit ranges impact the sounds. And I was able to change the velocity to affect the desired outcome.

Thank you.
Karl

PS — See my comment about a Montage boot camp (new post).
Cheers.