To elaborate:
"A Covenant that is activated or put in the Artifact pile can no longer be targeted as an enhancement and it is a neutral card with no brigade."
Under "use an an artifact" your third, forth, and fifth statements are incorrect <== Comment from RDT [mjb quoting not working]
So the REG entry should read...
A Covenant that is activated or put in the Artifact pile can no longer be targeted as **a curse or** an enhancement and it is a neutral card with no brigade.
Also I want to be clear about the SA.
When a curse has an SA that says "Enhancement: Does X. Artifact: Does Y" is activated as an artifact, I can no longer target it by a card that "contains 'X'".