You have a conflicting problem.
i.e. i log into mirc with the nickname: JohnDoe, but change it within 10 minutes to JaneDoe - is there a way i can tell when someone has done this?
You start off with talking about how you use the nick JohnDoe, then change it to JaneDoe. Then you end the question with is there a way you can tell if someone else does it.
So what does that have to do with if you did the /nick?
If someone else did it, add both JohnDoe and JaneDoe to notify. Then, in most cases, the server sends you their mask. If it doesn't, then do the /whois. So /notify JohnDoe and /notify JaneDoe.