See Modfications. Project Award Changes (PACs) is a legacy term. PACs were the modifications distributed in a legacy version of the eResearch Proposal Management System (eRPM) to identify any changes in terms and conditions, additional funding, time extensions, and other modifications (such as a no-cost time extension) after an award notice goes out. This document most closely relates to the Modification that is now requested using the Request Action/Modification.
The Project Award Change and the Modification should not be confused with the Post Award Change Request Process and Form (sometimes called a PACR).