Looking at a bike that has 16'' apes on it currently which just ain't my style. If I go to shorter bars, will I need to change out the cables or can I leave the extra length?

I'd probably be going to 12''. Technically I don't see a problem but aesthetically?

Sorry in advance if this is a stupid question.

 

You can leave them, but how it looks will be up to you. There shouldn't be too much slack if you route them in order to take up slack. Hard to say though until you do it. A lot of apes I have seen end up getting cables that are a little on the long side in order to ere on the side of caution, sucks to get new bars and cables only to have them end up being 1"-2" short.