This depends on how the creator has set the prices and how they plan to update their game. If you pay the price for the whole project, then you would have access to all files available, except from files that have a higher price set by the creator. Such files need to be purchased individually.
If a file with a set price is updated by the creator, I think everyone that has purchased it will be able to update, although I haven’t tried it myself. If the creator decides to upload each new version as a new file with a specific price, everyone would have to buy it every month, and there is nothing anyone can do about it.