How would I go about adding new NBT tags to a tile entity or entity? I know how to make them if I create my own, but say I wanted to add data to the vanilla chest that records the last person who opened it. How could I achieve that?

coremods

Hm, I was hoping this would be simple enough that it wouldn't come to that. I guess I'll have to go learn ASM then.

well in all honestly you could always use PlayerInteractEvent to check whenever someone uses a chest and keep track of every chest in the world and who use it last, then save the result when the server closes and load them when it loads, but i dont think that a solution that scales very well unless you know how to store all thsi information super efficiently