Moved to ePO as an appropriate spot.
For giggles - make a copy of the policy; modify the copy by editing an existing Low-Risk Processes by copying over ti with test.exe and click ok ... If that works, it's either an ePO bug or Low-Risk Processes has reached it's max
Hi what is your ePO build number?
EPO hotfix: HF1144868 is your solution:
ePolicy Orchestrator 5.3.2 Hotfix 1144868. This hotfix addresses the issue where the Save button is disabled when adding a process to the On-Access policy for McAfee Endpoint Security (ENS), McAfee VirusScan Enterprise (VSE), or McAfee Management for Optimized Virtual environments (MOVE).
Massive thank you, Nielsb. That's exactly what I was after. All applied and confirmed that I am now able to add process exceptions.