There’s basically zero chance you’d get released back to a fighter if you’ve already been trained in a heavy platform. It’s hard enough to switch platforms in the same MAJCOM, let alone cross-MAJCOM. Once that heavy drops your name in an FTU class with a fixed number of spots per year and spends time and money training you, they’re gonna want a payback in the form of several years of flying in an ops squadron, and then the functional will want to keep you as a body to fill shortfalls within the community or white jets. The “promise” of a going back to a fighter will be a long-forgotten empty consolation for your hard work in UPT that was made by someone who is now no longer in your chain of command.