[Sampsa]

Thanks Lynne for your reply, that's what I thought after googling, there is no ready solution.

I managed to do a workaround which seem to work. I created a style_fetch plugin with conditionals if styleid = light (1) and forumid = subforum -> styleid = light (4) and same thing with dark style. And another check when returning from subforum back to main forum: if styleid = light (4) and forumid != subforum -> light (1) and same with dark style. Finally I created a simple custom quick theme chooser to each theme