I was in our local (Edinburgh) Gilbert & Sullivan society for a number of years, including about 10 of their annual productions. The director would always add or subsitute in a couple of very topical lines, while otherwise sticking to the original script. Don't think anyone took offence at this liberty: on the contrary, usually raised one of the biggest laughs of the night!
In one production of The Mikado, we had characters bouncing in on space-hoppers, or sailing in on skateboards. And on one occasion, the skateboard continued its trajectory into the orchestra pit, narrowly missing the oboeist!