I spent like you hours trying to do this once when I wanted to change a userSettings value. After rigorious debugging I couldn’t get it…
If I recall Epicor does something like:
- Save userSettings into memory
- Download .sysconfig
- Download all files if needed and extract
- Put back userSettings from memory
I had to do it through Software Center, or GPO. Trust me, I tried for 2-4 hours, even to exploit it 
no go.
I even made a Deployment Package which extracts itself to the clients to /config/ dir (it worked) but the userSettings still merged After-Update since its like the “last action that happens”
No Go
