Custom part categories: where they are stored??? Is it possible to copy them from one game installation to another???

[Araym]

Preface:

I run A TON of mods.
Among them, "Custom Category Kit" and "WildblueIndustries", both affecting MANY new part categories appearing in my VAB and SPH, so I don't really know if any behaviours of my installation could differ from a pure "stock installation".

My issue:

To have a "better" way to find parts, in a custom made arrangement that fit my preferences, I started to split parts in various group using the stock "Add custom categories" menu (the last light-brownish option under the "filter" expanded part menu): it's a painful process, but by the time is proving to be more efficent for me, because both the standard stock groups and the various added mods categories in the blue-ish "filter by function" groups are, often, a mixed nightmare (if, by example, I'm searching for "jet engines", I have to hunt them in the common "engine" category, mixed with any kind of other type of engines - rockets, xenon, nuclear...etc etc). This is even worse for other type of needs (for "structural parts", I often need to jump between the "structural" category and the "aero", if maybe the needed shape could be a more classic "tube" put in the former, than a "conical shape" that could be a nosecone in "aero")
Sometime, using the "Janitor's Closet" mod and some in game filtering, I'm able to shrink the mess, but nothing is alike having perfectly, split, custom categories.

Fortunally, these categories, once made, are shared between all my saved games, so it's a one time effort...
... mostly...

The problem and the "help" needed:

... untill, for testing purpose, I find myself in the need to set up different installations of the game.
So I would like to find them and, someway, export them to a different game installation, to not have to redo all my customization from the ground.

And here my question:

As rougly knowingt how KSP works, when "saving" something, these "customized categories" should be stored somewhere very likely as a .cfg file (I see various mods using those to add their own "stock custom categories" that way).
They are probably not in the "save" persistent file, because I already know that my categories are "cross-saves" compatible, but I VERY FAILED to find them anywhere else in the game.

Can anyone help me, pointing where I should look ???

Thanks in advances.

Edited September 8, 2021 by Araym