I’m slowly catching up and I see that Inside Microsoft Dynamics GP has a look at a new feature to formalize budget changes in their new post General Ledger Budget Transactions.
General Ledger Budget Transactions in GP 2010
General Ledger & FinancialsGP 2010
Archived post from 2010. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.