Load the song, hold down Play/Stop All and then choose to delete all tracks (or do that any time after the song has had a track put to it). That should free it from a locked in BPM I believe. It works for me, but our situations may be different since I don’t use a BB, but I do rely on an external master clock for setting tempo in a similar way. The Aeros BPM will take a bar or two of sampling the clock playing from the other device to find the new BPM (at least with a master clock like I’m using).
Don’t do this for a song that you have saved that you want to keep. Delete All is like an auto save also, you’ll lose the song’s tracks on your storage device (at least that’s the way it is in my case running the latest firmware). This is a lesson I had to learn a few times before I realized what was going on.