I don't believe there is any way to define your own categories. You could use a naming convention fpr your performances e.g Split-PianoStrings and use that text to search in the category search window.

In order to assign one of the existing categories to a Performance, you need to change the category of the *first* part in the performance.

From Performance Home, click on the first part and press Edit. The Category and subcategory for the part can be changed at the top of the screen,

Yamaha uses mnemonics themselves to designate different things. I've suggested the same type of usage to others to generate your own category names.

Before, I suggested your initials then a couple more letters that mean something to you - at the front of the performance name so the category search would come up with your content first.

If your name is "Frank Morgan" (as in the late great alto sax player) - then this may not work out well since "FM" obviously may match lots of other stuff. But hopefully by the time you type more like "FMPS" (Frank Morgan Piano-String) it's unique enough to keep using your initials.

You can come up with your own convention - use initials or not. Maybe use a character like "!" as the first one or "#" since no presets really start with those. Then 2-3 letters for your category.

for an earlier take:

https://yamahasynth.com/forum/using-montage-category-search#reply-21238

This comes up often... you are given 20 characters to Name your creations - use them wisely. You can easily define your own system for listing the data ... let's state that the Category Search has a prime purpose "finding" your sounds. You can use whatever letters, numbers or characters from those available.

You might create a group of sounds that you refer to as "Butterflies in Space" (a favorite of many of the programmer folks)... (I'm sure "Particles in Space" is an inside joke referring to this category) - but just as an example... if you place the initials "BIS" as a prefix or suffix in your Performance Name then typing in the letters BIS in the Search box will recall all of your Performances. Spl for splits, Lyr for layers, etc...

If you wish to create your own Folders of categorized data... we highly recommend your computer for such listings. Montage Connect will allow you to create your own folder hierarchy and let you manage/organize your sounds quickly and easily.