To my mind, any specific problem you have whose solution involves you, the asker, actually picking up a tool and using it on your vehicle is welcome here.
I'm coming here to read and ask about doing the work; whether it's strictly "repair" meaning "get my car back to operational condition" isn't the important factor in my opinion. A modification is just a "repair" done voluntarily; to make the asker's motivation the determining factor for being on-topic is nonsense.
You want to replace your headliner with a tartan flannel sheet?* You want to install a stiffer sway bar link? You want to mount fins on the back? You want to change out your calipers for an enameled blue pair? These are all concrete technical tasks that I think would be interesting and valuable to have posts about. There's also plenty of overlap between "mod" and "repair" -- is there any meaningful difference between replacing your working calipers with a new pair that looks awesome and replacing your broken calipers with a new pair that just works? I'm pretty sure I can manage to follow a guide to the former when I need to do the latter.
A post about something done for enjoyment, instead of "crap, this is broken and I need to fix it!!" is refreshing, and it might even help draw new users. I'd be happy to see a crowd of mod-focused members here.
(I personally am far less interested in questions about paying other people to do the wrenching, although I recognize that's probably an unavoidable segment of the site.)
*My brother did this and it's awesome.