I discovered form personalization as a great tool for doing mass updates. I tried to change the priority of invoices group this time but when I move from inv_sum_folder block to payment_schedule block first one disapears and I am not able to move back. Basically in this case it was suppose to work like this:
1 query a group of invoices that needs to be changed
2 go to item payment_priority (what is equal to going to block payment_schedule) - here invoice block disappears leaving only scroll bar and record indicator
3 change value to XX
4 go back to invoice block
5 go to next_record
Steps 2-5 are repeated if invoice record exist where currently record indicator.
I would appreaciate any help as I tried everything what I knew and I could not ovecome the problem.