That's awesome to hear! It’s great that you were able to upgrade your 2015-2017 Mustang GT with the 2018-2023 MBRP Race Mustang GT catback exhaust and have it fit without major issues. The quad tip conversion definitely gives the car an updated, aggressive look that many owners prefer.
Checking for compatibility, Raceseng's reverse lock probably uses a "push" system or similar mechanism, which might be compatible with other brands' shift knobs. If you don't have luck with Raceseng, you might want to try shift knobs from other quality brands that use a similar reverse lock...