from having played with the game constantly in the last 3 weeks, I can confirm that rapid fire isn't an important feature, and if it's causing problems getting rid of it won't be detrimental to the trainers function tbh. With unlimited ammo and no reload, i can't see any actual use for it.
The reason why the plasma gun & the cryo cannon's Unlimited Ammo appears to not work is because they use a single "clip". Therefore, since the "No Reload" option fails, those guns simply run out of the ammo. There's no reload for those guns so they simply run out of ammo. Once the "No Reload" option works, those guns with a single clip (or magazine) will function as desired. There is no issue with the trainer's "Unlimited Ammo" feature. I hope this explanation makes sense.