Oh, are you 404? I didn't realise you'd changed your name.
It's a bit out of my ability range at the moment, but the plugin TF Econ Data appears to have a native for getting a weapon's possible paintkit definition indexes. If they use indexes then I suspect it would only be possible to have custom paints if the weapon models and materials were also custom. I say that in the hope that someone far more knowledgable will prove me wrong.
Yeah that's me. Not using the "404" name anymore, retired it. Just going by TF2CutContent now in hopes that it'll bring more attention to TCRF and what we've got going on over there. I'm mostly out of the TF2 community entirely at this point but obviously I've ended up back here after a while of being inactive which kind of proves me wrong about quitting the community, but oh well.
And yeah I've already prior made my own fake warpaint granting plugin in a similar vein to Skials' fake items. Making a plugin to give yourself fake warpainted weapons was easy enough for the first set of warpaint weapons since those had their own item indexes. The newer ones don't use that same initial setup and instead use an entirely different system, but it was still possible to generate fake versions of those newer warpainted weapons as well. So in closing, giving yourself fake "official" warpaints is definitely possible, I know that much for certain. Using custom textures for your own custom warpaints though, that's a whole other can of worms. I know the new warpaints are handled via attributes that are assigned but I'm not sure if it's possible to inject a custom texture into the list of existing warpaints to have it be "usable".
And I'd like to think that I'm that "more knowledgeable" person but to be fair there's way smarter people out there like mastercoms. I do know the engine pretty well though. Pretty well enough to be able to discern (in most cases) if something is possible or not.