Not sure about changing before hand, but I’d say no at meeting. They’d have to know exactly how you voted to cancel those votes - you’d have to download how you voted using the code and ID the present how you voted. If you didn’t do this, you could just vote for A, B, C, D, and E, say you revoted A, B, F, G, & H … thus removing votes for someone you didn’t like then vote for D & E again - effectively getting four votes: two more votes for D & E and taking away two from someone you didn’t like. twice.
In general elections if you send in a mail in ballot you can’t change your vote. So I’d say if you voted electronically, when that closes you vote is permanent at that point…