I have a Marauder F & T in 177 that was fairly early on in the production, bought late 2018. I have spent a significant amount of time tuning and fiddling to get it shooting the way I want it to. When i got mine I called Crosman and asked one of their techs a bunch of questions about the 'factory tune' that was on the gun as shipped so I had some idea where I was starting from and how to get back there if I ever needed to.
My experience is that you will have trouble getting any significant power gains out of it without bumping up the reg pressure. And even after a reg pressure increase there are still very limited gains to be gotten due to the painfully small amount of plenum volume available in the design. At the factory reg setting (2050 PSI according to Crosman) I could not get the gun to shoot 20 ft/lb with 13.4 gr pellets. Transfer port wide open, hammer spring max, hammer throw max, the end of the world for me was 780 FPS with the 13.4 grain pellets (18 ft/lb). Yes I did bump up the reg pressure on mine to get to the tune I wanted (810 to 815 fps with 13.4 pellets) but the gun is still highly limited by the plenum space available in the design. It's unfortunate.
I have an 8 page MSWord document with all my notes of things I have tried over the last 4 years with that gun, so it's not like I haven't spent some quality time with it. I guess my point is that if you are looking to make any significant power gains with the F & T Marauder in 177 you might have better luck looking elsewhere. Just my opinion from my experiences.
Good luck with whatever direction you decide to go.
