You ask reasonable questions.
1.) The gun is better now than it will be after any modifications. Modifications will destroy the gun's value.
2.) Nothing ever got stronger by removing metal. Shadetree American gunsmiths have caused more danger and destruction of value by lengthening chambers than they've done good. Equally unadvised, you can shoot a 2.75" shell in a 2.5" chamber. It's very dumb because it causes a pressure spike, but people do it. Slightly less dumb, people will lengthen the forcing cone to shoot 2.75 low pressure shells in a 2.5" chamber.
3.) Presently, the cost of 2.5" shells is an astounding $12. I believe the cost at present of 2.75" shells is roughly a cent less per box.
4.) 2.5" shells pattern better.
5.) 2.5" chambered guns are about 1.5lbs lighter
6.) 2.5" chambered guns are worth considerably more
7.) Guns that have been lengthened from 2.5" to 2.75" become virtually worthless, particularly if they are not re-proofed in England afterwards
If you want overweight guns with lots of recoil and poor levels of refinement, just buy a new 2.75" gun. Doing such conversions to this gun is equivalent of buying a ferrari and putting a trailer hitch on the back.