As far as helmets for racing, I use an open face helmet because I can put it on a lot easier. I think my next helmet, I'll go with a full face one. I just pull the lining outwards to slide it on over the processor and coil. There have been a few times when I put my helmet on, the coil slides and causes distorted sound.
Otherwise, I have not cut out any of the lining.
There is another racer who has a CI and she takes her processor off when wearing her helmet. I can't do that since I listen to the engine and tires a lot. Seat of the pants works if the car is loose and wanting to spin.
Good luck and if you have any specific questions, ask your Dr.
BTW, I have been told that I don't have to be overly careful. The internal processor if it is going to get damaged, I'll have other problems like a fractured skull. Of course the external processor is a different story.
Good luck and have fun playing this summer.