That shouldn't be a problem, because the wear levelling algorithms of the flash controller would take care of it.
OK, hypothetical situation. Say the flash disk is completely full of information, but just a few bits need to be changed often. What is the controller going to do? If it uses a different spot to put the new information, that means it has to write over some other data, and if we don't want that data to be written over because we might need it soon, where's it going to go? Somewhere else, over the top of something else we might need?
If the disk is full, any wear levelling methods won't work. The only way they can work is if a large portion of the drive is left empty, so new data can be written over empty cells, and where the original data was can be left until the wear levelling algorithms say its that bit's turn again.