I changed mine. I got paid on the same day every month so wanted the monies for this and everything else (council tax, rent etc.) out of my account so I could budget with what was left. . Wasn't a problem. The V in IVA does stand for voluntary after all. Cant see the IP having a problem with it and I'd be surprised if they did.
Sharing from experiences of dealing with debt
The greatness of a man is not in how much wealth he acquires, but in his integrity and his ability to affect those around him positively.
Bob Marley. http://kallis3.blogs.iva.co.uk
During my IVA I started a new job that had a different pay day to what I started with, 4th of month. Changed to last Friday of the month, when I phoned my IVA company there was no issue in changing the day of my payment.
Last Payment made 04/12/14. Completion Certificate 25/7/15. IVA company GT. No Issues