You can usually cut your own post provided you have enough cause. For example, if you're posting your character taking aim and shooting a character in the head and their head is immediately behind cover, you can't realistically expect the character to aim up and shoot thin air.

Basically, you can interrupt your post if your opponent does something which significantly interrupts your post, or if you leave an 'if' statement like Khan likes to do to specify when his character would do something different.

Personally, this problem is pretty much the main issue with post-by-post arena RPing in my opinion.

I also just realised what thread this is in, and that I'm still subscribed despite not being in it, nevermind, still posting.