As someone who was in the school edition production (as Cosette) and a huge fan of Les Mis, I can say for sure that the show is great to perform and is good for younger students as a first show. (That may sound weird, but there were many ten year olds who joined the theatre group for that show.)
And, the only things we changed for Mme. Thenardier's lines were:
"lifelong twist"
and "everybody raise a beer" "raise it up the master's rear" =)
I get lost, unless, of course, I'm getting found.