You need to check the T&C’s with each site. Some do seem to suggest that they need to be told of the deal at the very last.
Additionally, there seems to be a zeal amoungst some groups to weed out non-performers – specifically they really only want affiliates who are bringing new players as well.
A result is some pretty draconian wording around loss of revenue if a new player is not brought in every month. So make sure that you’re covering all the deals with your existing sites.
EDIT :
And then of course the program may want to “bundle” the accounts with your existing accounts too – so it could be a bit more problematic than first thought.