So yes, you're changing FIFO and it is not for the faint hearted, but often with FIFO, you've got like five on five off or whatever that might look like.
When you enable high-throughput mode, SNS FIFO topics will maintain order within message group while reducing the deduplication scope to the message group level.
Whereas if you find that because you're FIFO, perhaps you're already a little bit more isolated, the move may not be as taxing on you or it may not be as hard to move away from that circle.