Sorry, I don't really understand your second idea. Can you explain it more comprehensively?
Try using the "reply" button at the bottom of messages, so Itch lets that person know that he has a reply.
Back to the topic. Don't change your current game page, create a new one that is free (PWYW) and leave the other as "premium", Itch allows you to have 2 versions of the same game, as long as one is free and the other is paid (premium content).
In your second part, you put a sale with a discount and with the condition that they must have the "premium" version of the first game.
That would be enough. But if you want to be a little more elegant, you can hide the premium version, that way, anyone who searches for your game will always reach the PWYW version, and on that page, you create a link with all the information and advertising of the benefits of supporting you by buying the "premium" version.
Ohhh, sale conditions. That's what I was searching and missed.
Depending on the time scale and when projects get set to pwyw, the interface would just not differenciate between a minimum price customer or a pwyw customer. So a coupon code as a individually priced text file might do. Honestly, who is gonna support indie games and would cheat on discounts? One can limit the number of sales through this coupon to 2x the number of customers or some safe number. And hey, if the thing is so popular that people try to cheat a discount just to read it a few weeks earlier, at least it is still money they pay, instead of waiting and reading it for free.
Sale conditions
It’s possible to restrict who has access to the discount provided by your sale using a Sale condition. They currently come in two forms: coupon codes and ownership requirements.
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From the sale edit page, select Add condition and choose the project that must be owned for the sale to be active.