Looking at the comments in this thread, there seems to be a fundamental problem in understanding between the way traditional theorists view time signatures and the way modern ones do.
If you're writing music that conforms to traditional standards, there are clearly meanings behind certain time signatures like 6/8, which implies two sets of 3. From a modern perspective, it doesn't have to mean that - it could be 1+5, 2+4, 3+3, 4+2, or 5+1. In fact, there is absolutely no difference between 3/4 and 6/8 besides which size note gets the beat - but we've assigned relevance to those signatures through history, one meaning "in 3" and one meaning "in 2".
To answer your question, 4/8 (instead of 2/4) specifically has no historical relevance, so you're probably safe using it in any context if you want. If the eighth note is more important or the tempo feels better with 4/8, use it. If you used 6/8 (instead of 3/4) like that, some people may not like it.
Personally I don't really care for the idea that 6/8 is fundamentally different than 3/4 (and by extension the idea that accent patterns should affect time signatures by default), but I'm not going to argue with those who do. To me, the relationship between the numerator and denominator should strictly be # of beats per measure/which note is assigned the beat. Accent patterns need not have a place in time signatures - that's what accent marks are for.