Can you overwrite a business on desktop with a new import from another computer?
No, when you do a “add business” “import backup” it creates a new business but with the same name, therefore you should rename your existing business before doing the “import backup”
Is it possible to add an overwrite function?
No, Manager is designed to always creates a new business when you do "import backup"
If you were allowed to overwrite and then discovered that you had overwritten the wrong file, you wouldn’t be able to reverse the process.