Add these to your backpack, rename var_setters 1-3 to whatever you like, and use these to make dynamic variables, useful for all sorts of things! I haven't tested these fully so if anything doesn't work please tell me.
I made this by directly modifying the project.json file, very easy and simple to do, surprised that there's not many of these out there. I saw this being done in Scratch 1.4 so I decided to do it in 2.0 and it's easier to do than ever. If you use any of these blocks to make a project please send me a link to the project, I want to see how they're used :).