https://itch.io/docs/creators/exclusive-content
"you might give buyers the opportunity to have a character in your game named after them, but you only have a dozen slots. You can create a reward and set the quantity to how many slots you have. Once the reward is sold out it can not be purchased anymore. You're free to adjust the quantity remaining if you discover you can support more.

The reward editor lets you specify a custom field to collect from the buyer, you can use this to collect the name the buyer wants to use."

Just to confirm, this means that you could take that custom field data and manually add it into your game, then update your game, which would then become available to everyone who downloaded it from then on? So everybody would then see that character name?

Is it possible to have it so that the buyer can purchase a customisation for their game alone? For example, they could perhaps name the main character in the game, and whenever they download the game, the main character would have that name. But for everybody else who downloads it the main character would have a default name, or - if another player had purchased that tier, then they would see the name that they had selected?

I suppose the reward option could be unlocking the ability to name the main character whenever they start a new game, although that carries less weight than purchasing just one specific name.

Do the game files have any knowledge of what data was entered into the custom field?