Yes, there have been a few fix-ups on DT's live albums over the years, although MP has tried to stay away from the studio as much as possible since Live at the Marquee.
LATM: A significant chunk of the vocals were overdubbed, as well as some of the guitars.
OIALT: I'm unsure if there were any overdubs on this album, but Derek points out that there were no keyboard touch-ups at all.
LSFNY: JP's back-up vocals in "The Silent Man" were re-recorded because he sang the wrong lyrics on the night. There was also a screw-up in "Through Her Eyes" which was not fixed because Mike wasn't available on the day the overdubs were recorded (both his and JP's back-up vocals at the concert for that song were through the same mic, so it wasn't possible to just re-record JP).