When selecting multiple instances of a variable using Ctrl-D, my expectation would be that any transformation applies to all selections. This doesn’t appear to be the case when invoking the ‘Convert Selected Text’ command, e.g. change to upper-case using cmd-U (on a Mac). Only one of the selected items will be affected. I think that this is a bug.
It would furthermore be nice to be able to edit only parts of a selection instead of affecting the entire range; e.g. change a variable name in multiple place instead of replacing the entire name.