if someone painted up the marneus calgar model as an imperial fist, I'd laugh, and move on. If i spend 14 hours converting and greenstuffing a figure to use Pedro Kantor's rule and to paint up in my Aurora Chapter colors (which I did) and he looks nothing like Kantor, but has the right equipment and my idea of the Aurora chapter master fits with Kantors rules, Im doing it (and I do use him).
Stop thinking about them as special characters, and start thinking about them as specialist HQ choices. Thats what I do. After all you will be seeing them, so get used to it.
"And the seventh angel poured out his vial into the air;
And there came a great voice
Out the temple of heaven, from the throne, saying: It is done."