Help with code

[RawCherry]

I'm trying to fix a mod, I already have in mind how to solve it but I don't know how to do it specifically.
I would like the trigger codes (I imagine it is a trigger), example:
execute this when the world is saved, when it changes phase, when season is changeg, when the world is initialized.

I would also like to clarify a doubt, if it is possible to store the value of a variable in another file (lua, txt or any other format) to be read again, for example: save value x in a file after the world is saved or before it is closed , when it is opened again read the value stored in the file