Purchases are project based, not file based. If I give you money, I own access to your project, even if you later set a minimum price. It is the same with a sale. If you have a paid game with 20 $ price and make a sale for 2 $, the people that paid 2 $ still have access, if the sale is over.

If you want file based selling for an ongoin development project you should rethink your approach. What you sell is an early access game in beta or probabla alpha or pre-alpha stage. People excpect updates and the finished product when they buy.

Itch should add some ongoing support possibility, instead of driving people to subscribestar or patreon and all the other less known platforms that can do that.

Unfortunately, itch has something called individually priced files. It creates a lot of confusion and harm. It is not as the name says individually priced files, but a donation level. A level you cannot increase! You can set this level to give access to files based on that level. But as long as itch does not fix this feature, it should not be used. People cannot increase their level. They would have to buy again.

People abuse this feature to appear in free games, but still have a sale price. They should just make two projects, one free, one paid. Or include a public version as a demo in their paid game.