Custom Gunsmithing of the BHP is a bit tricky, and sending it off to a specialist would be advisable.
If you're looking for some very basic stuff, you could get by locally. Mainly, get your sight cuts done at Angie's. Buy a firecontrol kit from C&S and drop it in yourself.
Much more than that, such as fitting a barrel (or even a bushing) would need to be sent off. I wouldn't let someone local stipple a BHP for me, let along checker one. The other nice touch I've seen done to BHPs is a welded on beavertail. There are a few outfits that do this, all of which would require shipping.
If you're going to send it out, I'd strongly suggest Jim Hoag in California or Bill Laughridge's Cylinder and Slide. Both of these guys have tons of experience with the HP and turnaround times are more than acceptable. Many other smiths that specialize in 1911s also do BHP work, but many times not as well as the first two listed. Mark Morris, here in Washington, is one of the foremost 1911 smiths in the world. His prices and backlog would support this claim. He says that he'll build one BHP a year. He likes the gun, but conceeds that it's difficult to work with, as tightening up the frame to slide is difficult, especially since the transfer bar rides in the slide.
I've a couple of BHPs that have been customized. At the 2003 SHOT show, Wayne Novak, Joe Bonar, and Pete Single just about talked me into buying a BHP that they collectively worked on. It was nice, real nice. Price tag was $3500. I had the money at the time, but just couldn't do it. I was kicking myself the minute I didn't buy it until I was able to settle that urge with a pretty nice Jim Hoag HP. The particular Hoag HP I have is nicer than the C&S HP I own, but either would work well for just about any assignment.
If I would have known that Joe Bonar was going to get killed this year, I probably would have shelled out the coin, just because that gun can now never be made.
I know this is a bit of rambling, but I hope it helps.