What will happen if someone mods eg bat sponsor,
I imagine it would be a localized mod, so however you mod the game on your machine wouldn't effect anything in the Academy or the Online gameplay components and would only be visible to you.
Whenever I've done mods, I've often included a readme .txt document to let people know which kit items to replace, that way it's easier to release updates to kits if people follow the instructions and replacing certain elements (and having people make complimenting kit elements) is a whole lot easier. When I moved to making bats, I just created an excel file of all the bats in the game and what I was replacing to keep track of it, that way when I changed a player in the squad-editor, I had the excel file open in another window and knew which bat to select for the correct sponsorship.
So it's easy to keep track of locally, a little harder when there's lots of people doing the same stuff, hence why I pretty much stuck to modding kits as nobody was really doing it and I suppose most people ended up downloading my kits and replacing them with the updates when necessary so it became self-managing. With this game it might be a little different as to how certain element are replaced, based on the editor inside the game. We'll have to wait and see how that works, but just looking at the visuals, I think bat logos will be reasonably easy to mod, as will sponsor and team logos.
Overlays and actual kits will be a little tougher, there's a lot of stuff at work there and doing the little niggly graphic stuff on, say, the NZ kit with the silver-fern across the lower 3rd of the T20 kit,
could be complex...