in ePO 4.0, it looks like the default for the inactive agent cleanup is 30 days. is there any way to change the number of days? I'm migrating to a new ePO server so it would be beneficial if it removed them after a shorter period, so i can see which ones are still pointing to the old server or not.
Yep, this is easy to achieve. The inactive agent maintenance task gets its list of machines from the "ePO: Inactive Agents" query, so all you have to do is edit this query and change the filter to whatever timeframe you like.