When one opens an existing file written by a different party, puts in a fix that matches the style of the initial author with no traces left behind (except cvs knows :) )

I see good and bad with "Ninja Coding."

the good

When maintaining code other folks code I'm a very ferverent believer in the concept of "First, do no harm." If patching you do improves the code and you end up leaving no footprints behind then all is well. Having said that leaves me a very good seque into the bad

the bad

If you patch somone else's code and an unforseen consequence of that patch comes up then you need to be in a position where you can be accountable for that patch. Not for the purpose of guilt, punishment or anything negative like that, but more a case of being able to answer the question "OK, what did you do and where?" Trust me, I have a PHB that modifies my code (and the code of other co-workers of mine) without telling anybody what he did and things break usually in the wee hours of the morning. PHB doesn't even use CVS to track his change.

When coding in a cooperative environment it is a good thing to maintain lines of communication. So if I change someone else's code I usually put comments in that explain that a) I did it, b) what I did and c) what my rationale was for doing it. Sometimes I've had to modify someone's code due to a bug report or a service ticket so I put the MR or ticket number in the comments as well as in the CVS log message.

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Note: for those not exposed to Dilbert®, PHB means Pointy Haired Boss.