After all, reality is entangled and there’s no well-defined framework of physical law that allows FTL travel and also reduces to something like relativity as long as you don’t turn on your magical engine. Everyone who doesn’t have a magical FTL engine would still see your FTL travel as being time travel, and the same questions would have to be answered as you raise below: what changes are allowed, etc.
This is a popular but incorrect idea. If you interpret special relativity via (neo-)Lorenz Ether Theory, you can have perfectly mundane kind of FTL without any problematic time travel, you’d just have a preferred reference frame. It’d be possible to send messages to the past according to some reference frames (in spacelike fashion), but not others, and you’d never get to communicate information in time loops. There is no serious problem with reconciling FTL and special relativity, FTL goes the way of ether for Occam’s razor reasons, not because it doesn’t make sense conceptually.
This is a popular but incorrect idea. If you interpret special relativity via (neo-)Lorenz Ether Theory, you can have perfectly mundane kind of FTL without any problematic time travel, you’d just have a preferred reference frame. It’d be possible to send messages to the past according to some reference frames (in spacelike fashion), but not others, and you’d never get to communicate information in time loops. There is no serious problem with reconciling FTL and special relativity, FTL goes the way of ether for Occam’s razor reasons, not because it doesn’t make sense conceptually.