trimming

I want to use my stock engine cover but have a air intake so I cant. Some guys have trimmed theres to fit back on but removed the material so that the air intake isnt in the way. Has anyone done this and what can you tell me before I start cutting thanks martin

Has anybody trimmed the door panel pieces on their door cards? I have taken out the central bit (where the handle is) but I had to break the plastic bits on the back to seperate them! Has anyone got any advice how to fix the piece back into place. I tried no more nails but it's not strong...

Want to remove/trim the fender lining so my wheel does not rub under heavy loads have coilovers. Will anything bad result in this?