So I was wondering if someone were to take your avatar image, and utilize it in a darkness message as their own does that fall under the :
“Impersonate a member of the Combine for any reason. This means you may not pretend to be another member over any communication mediums such as e-mail, IRC, message boards, MSN, etc.”
“Manipulate the game engine in order to hide or change your current in-game status. For example, you may not use a Star Destroyer custom picture on a Y-Wing or use an avatar picture showing you are under arrest if you are not.”
In all fairness Jev, the rules don't say "successfully impersonate." If you go on IRC as a random name, and pretend to be Seele, that breaches the rule.
While the Avatar would change, the content of the message wouldn't.
If you have a) content of the message strongly suggesting it's designed to be coming from e.g. you, and b) either a screenshot or confirmation from the recipient that the avatar was changed to your avatar, it's something that I (in your position) would at least submit a support ticket to have the ASIMs take a look and talk to the people involved.
If someone simply uses the same Actor/Actress for their character as yours, it's definitely not a problem. I would view specific copying of an avatar (including copying of the Faction Frame + the same actor/actress) as demonstrative of an intention to impersonate (and therefore explicit breach of the Rule).
Trying to find out when would be a good time to bug an admin about how a couple of open tickets, one pertaining to this matter and another to traveling? Anyone have a good idea of when they are about online?