Can existing games be imported?

Can and is there any way to edit games already created to edit them and make a mod of it

Sadly, it is not possible to modify an exported game, as the events are already compiled into JavaScript, and this conversation is one way only.

If you just want to make mods and know how to code in JavaScript, you can look into my project GDMod, a mod loader and modding api for GDevelop games.