migrating to a new machine, backup is duplicated I do not believe the Export and Import do anything with cloud storage accounts. At least from what I see in the product - only local accounts are exported since they have no credentials. It's backup / restore plan focused. The prefix is not a part of the backup plan. It's a part of the storage account.
So, let me ask: Where are you backing up - storage type?
There's a backup storage option on the left in the Linux UI.
As far as uninstalling, many ways in Mint. Find the item in the start menu and right-click uninstall, use software manager, use the command line. Your backup plans will be preserved on uninstall, but if you are concerned, simply export them first.