From what I've read, I'm not sure 1/2-3/4" will make much of a noticable difference on the rudder. Typically, rudder mods on the Tigers are more like 1-1/2 to 2". The elevator might make a difference with 1/2-3/4", but I can't speak to how much yet. If you've been following my build, I effectively added area to my elevator by moving the hinge line forward and eliminating the trailing edge tips from the stab.

If you are just going to eliminate a bay, do it from the outboard end, not the middle. You need to keep the inner rib spacing so there is something to glue the outer edge center sheeting to. I did mine the way I did because I was concerned about maintaining the strength of the wing as I intend to use this plane as a pattern trainer, so the wing will more than likely be stressed beyond the loads incurred by average sport flying. Also, if shortening the wing you might want to consider moving the aileron servo mount inward to keep the linkage close to the center of the aileron.