please dont answer unless you know what your talking about.
I am curious as to if I were to cut my headers and re-weld them in a way as to which cylinder 1 and 2 were directed in to a single exhaust on the left and cylinder 3 and 4 were directed to another single exhaust on the other side of the frame. (this is using 2 2011 yamaha R1 exhaust tips as the pipes. Would I make or lose power? would it mess up my back pressure? any insight to the effects of this mod would be appreciated!!!

 

its a fuel injected bike so back pressure isnt the most important thing in the world. I would make the split after the 02 sensors. like with any full exhaust a tune would be beneficial.

just my

 

in theory: you would lose back pressure, and therefore, compression and power. Aside from that, you're bike would be heavier, and the balance will feel different. The plus side is that you will look cooler and get more action.