Should I accept suggestion to move my name to the front in a field where authorship is usually alphabetical? I work in an area where most of the time authorship is ordered alphabetically, but sometimes when some authors contribute more than others, ordering by contribution is possible. I'm writing a paper with a former professor and another student. My name is often last when ordered alphabetically, but the professor suggests that I move my name to the front because I contributed more.

Should I accept this suggestion? Of course, moving my name to the front would emphasize my contribution for this paper. But when people see my CV as a whole, might they think that for other papers where my name is last (because the names are ordered alphabetically), it is last because I contributed least?
I think you should be honored and flattered by your professor's suggestion. He/she thinks you deserve a larger share of the credit for the paper and is trying to help you get that credit.

Your concern about the CV/publication list is somewhat valid, but there is a simple way to address that issue. In your publication list, put a small asterisk next to the paper in question, accompanied by a footnote saying: "For this publication my coauthors agreed to name me first author as credit for my contributions. In all other publications my name appears in alphabetical order, as is the custom in my discipline and indicating roughly equal contributions from all coauthors."

Of course, adding such a footnote is a bit tedious and awkward, and the benefit you will get from being first author may not be very large. Perhaps you may conclude that it's not worth the hassle. Or you may feel it could distract people looking at your CV from other things about you that you feel are more important. Or you may think this is just too trivial an issue to care about. All of those would be completely reasonable reasons not to accept the offer. But there would certainly be nothing wrong with accepting it.