I've noticed that there are a couple of posts like post #865756 or post #957157 that use variants of tags that seem to be fairly widespread like shaded (soft_shaded) and gradient (gradient_theme).

soft_shaded might have some merit, but I really doubt that it adds much to the ability to search for that kind of stuff.

gradient_theme on the other hand doesn't offer much so far as I am able to tell.

I haven't been very active on this site so far, but I decided to try to take an interest in it, so I'm not entirely sure about the etiquette of removing tags that haven't existed before or changing them to the more accepted version.

Is there a particular rule for this sort of thing?