I don't think it is unprofessional at all, I'm sure they understand people's availability etc changes from application to being offered. The worst they can say is no - I doubt it would negatively any decision about you. I've asked to change from VS to TC for two firms, one was more than happy to and one said they couldn't but gave me the option of continuing the app or withdrawing.Is asking for the possibility to move scheme dates unprofessional and/or risky?