The Lost Bayou Ramblers do this on their Live at the Blue Moon CD. On "J'ai été au bal" they switch keys in the middle, and then switch back. sounds awesome.
I gave up before I started. Speaking of changing keys, Marc Savoy plays J'ai Passé Devant Ta Porte in 3 keys, are there any other songs that can be played in 1st, 2nd, and 3rd?
Switching keys between comes easier for me going between C and G, for some reason, it's hard for me finding transition notes between F and either G or C, I guess because important note missing (?). I suppose with a band they can add the transition sometimes.