I did some mods to my Bb and C and have a few more in the works. The first thing I did was put amado water keys on them. They made a subtle but positive different in the way the horns play. Nothing drastic or even very specific, they just blew a little easier. I'm also planning a new leadpipe for my Bb and perhaps my C if the first one goes well. I'll let everyone know when I go through with it. I'm waiting on GR's leadpipe so I'm working on his schedule and not mine.
Heavy caps are also a possibility.