After digging in the source, I will tentatively say it looks like imported keys never go into the keypool, which is where change addresses are drawn from. Just keep this in mind: nobody designed it to securely handle the situation of a known private key. IMO that seems reason enough to not chance it. cp1 has a good point about different versions behaving differently, too.
I assumed that with things like cassius coins, people now expect an imported key to be "safe to import", and future versions would try to keep it this way... I admit though it's probably better to start fresh and not take any chances... I just wanted to see if this was URGENT , or safe to do "in the next few weeks"
