I tried just leaving off the value thinking that `-custom -prop1` might display prop1 instead. But it doesn't.
I did manage to figure out that they are stored in the SQLite3 database /var/McAfee/agent/db/ma.db, but I would like to avoid doing something like the following to see if a value has already been set to the value I want it set to. Installing sqlite3 on all of my systems only to find a custom property.
sqlite3 /var/McAfee/agent/db/ma.db "SELECT COUNT(*) FROM AGENT_CHILD WHERE NAME = 'UserProperty1' AND VALUE='Foo';"
I can grep for it, but that seems gross also because I would have to make sure my custom properties are unique as to not collide with other strings in the file.