Practice both!!! I play both very regularly and have no problems with adjusting. If anything it has made me more versatile! I can pick up pretty much any guitar or bass and feel comfortable enough to perform live with it in 2 minutes.
I have found that my guitar solos sound more like bass lines, though. But that's probably because I was mostly needed and known as a bassist until just recently.
Piano, melodica, trombone, uke and hand percussion all come pretty easily to me too. Learning instruments is like this: once you learn how to play two well, you can make pleasing noises with pretty much all of the others with little effort.
Fretless club #585