Not always. When Merrill Ashley was having trouble with the repeated double fouettes in the turning variation in “Who Cares?” originally danced by Marnee Morris, she asked him if singles would do if she did them with special speed and brio and he said, “No, dear, doubles.” She said that if a dancer made a genuine effort at a difficult step and still couldn’t do it, he would make a change, but not before the dancer had really tried. It is true on other occasions that he would just change the step. Of course, those were his own ballets.
Certainly changes and adjustments happen over time, but it seems to me that steps that have become closely associated with a ballet or a role should be made with caution. I am not crazy about hops on pointe, but I would miss Giselle’s (and Ashley’s in Ballo della Regina).