In a car requiring 92 or 93 octane and 94 pumps arnt always available, would it be possible to use 91 and an octane booster for a tank here and there?

how safe would that be or will there be detonation issues?

 

Yes, it's safe. But you are guessing on what your actual octane is when you add it yourself. If you have ever been to a Sunoco station, you will notice that they have only one nozzle, yet you can pump a half dozen different octane levels. That's because the pump actually meters in the additives.