I can't quite figure out what you mean.
Did you 'cite' artillery as your occupation choice or did you 'sign' as an artilleryman?
In anycase, your best bet is to ask someone at the CFRC.
From what I was told during my discussions were this:
1. When it comes to changing your occupation choice during the recruiting process (before accepting a job), it isn't too hard. Although I haven't taken one position out completely, but lets say you have Infantry as your #1 choice, you can move that around quite easily. Or at least I had no trouble because I was able to put Armoured and Artillery in as choices right after I wrote my CFAT and was told the Infantry hiring may not take place for awhile. That was my experience at least. You should still ask them though!
2. When it comes to changing once you are hired, I was told that it all depends on the Army's needs... So ask'em. There's a beaurocratic process that takes place and some trades are easier to get out of and/or get into. For instance it can be harder going from Support positions to Combat Arms positions and vice versa. It really just comes down to the Army's needs. Like was said though, you should ask. They were quite honest to me about what I would likely be able to do and what would be hard to do.