I came across this answer some time ago, and upvoted it because it seemed generally accurate and helpful. In recent days the tags on the question were edited and the question rose to the top of the pile, and I had an opportunity to re-read the answer.
The answer still seemed broadly correct, but on further examination I found it was not completely accurate and a little too narrow. The issues were not dealbreakers—they seemed like minor mis-phrasings or oversights, which were understandable as the answer was not written by someone who had personally worked a Clearance Delivery position. Rather than creating my own answer which would have restated almost everything found in the first one, and would have "competed" with it, I opted to add my own information and corrections to the existing answer.
My edit was rolled back to the original version by a third user, with a reference to this Meta question regarding an answer which had been expanded from seven words to 108. I feel like this was not taking my edit in the best of faith; while I admit to some re-shuffling of the answer, my edited answer clocked in at 229 words compared to the original's 186. I feel like I did not modify the meaning of the original answer; instead I corrected some errors in understanding and expanded the its scope to refer to all airports, not just towered ones (incorporating information present in the comments). I feel like I made a substantial edit and left the post better than I found it, as prescribed in the help center.
Did I overstep, or was my edit in line with site guidelines and normal use of the edit function?