I always change tuning from EADGBE to DADF#AD after the cigarette break. Then, after three or four songs, I turn it to DGDGBD, and after other three or four songs I go back to the EADGBE and keep that till the end of the show. All with just one guitar. Some years ago, when I began performing at pubs, it seemed very difficult to get a satisfying intonation in a very short time, but I took it as the only way to get skiller (?) every time. At present, I can change the tuning while announcing the next song, but the target is to do what I was told John Renbourn does in a really easy way, wich is to change the tuning of just one or a couple of strings while playng the song. Cheers.