The TC FX changing app works pretty well, and only takes a few seconds to implement once you've got the hang of it, but you do need to hold the phone over the bass pickup with the phone's speaker on for a couple of seconds, so it's more a mid-gig break task rather than in-between song type of thing. But in all honesty, unless you wanted chorus, flanging or distortion on your bass, I'd stick with one of their compressor programs, Their multi-band one is very nice indeed.