Jetset320
You'd have to examine the landing CoG, without a specific example I'd say that once in the cruise the pax could move around but they would more than likely have to resume their seats for landing. The pax may have been moved to satisfy a landing trim problem not a take off problem.
The zero fuel trim, of course will not change, but the actual CoG will change as fuel is burnt off. It usually moves forwards.
Regards,
BH.