Hey, how would I get around to getting the user to do something and then affected other instances of program, for example. Mario maker levels or clash of clans base’s, Creating a object and sending it to other users.
Depends totally on what you’re customizing. Obviously the most simple would be to change the color of an item, save the color values to some kind of file, get it to the other computer, read the in, validate them, and make the change visible somewhere.
You would need to code all those steps, including user interface.
Going up from there you could take it all the way to making your own 3D editor and file saving mechanism.
This is not a trivial task.