Can I bypass my 4wheel drive switch so I can get truck in 4low

No. Go to a junk yard. They should have plenty.

The whole thing about using the a/c is close to false. The only reason you use more gas using it is because yourban working the motor a little harder. Maybe a thousand rpms and that's just with the older vehicles I'm sure newer ones 08 maybe 10 and up use a method where it doesnt make a difference at all

Yes you can but u need a double pole double throw toggle switch and it's tricky