Can "edition" be used to mean "the act of editing/changing something"?
Your colleague is correct. Though it would make sense for edition to mean editing, it has come only to mean the result of the editing (e.g. second edition) or the format of the finished work (e.g. leather-bound edition).
It would be better to use editing or revising.
I would recommend the term "emendation" for this purpose.
For example: "Emendation of the injured text was made to restore sense."
More examples here.
The advantage of using "emend" in this way is that it is often more value-neutral, where "edit" has a somewhat critical nuance that may be unwanted.