Hello. I would like to do a HQ texture upscale.
Is there a way to replace sc2 textures for arcade and coop?
no, because your mpq would no longer match others mpqs and you would probably crash.
you can make custom textures for your own arcade experience, and your own maps, but the other projects by blizzard and other content creators, would not be changed by your changes.
If you want to make your own custom campaign experience, with higher rez textures, you would have to create a package similar to lorddbz who made the multiplayer campaigns, and edit your primary dependency, then use it in all the campaign maps the way he did.