But I *still* can't understand, which rule prohibits us writing:

romuluSnganpu''e' chaH jaghpu''e'

As for the enemies, they are the *romulans*

i.e. placing an emphatic {-'e'} on the first noun of a be sentence.

There's no known rule against it. However, the first -'e' would have to be interpreted as focus instead of topic, so the meaning would be As for the enemies, they are ROMULANS (not somebody else). In other words, the topic jaghpu''e' tells you what the sentence is all about, while the focus romuluSnganpu''e' specifies Romulans instead of someone else.

However, if Klingon had a rule which hadn't been mentioned yet, this would be my vote. I think it's very possible that Klingons just don't use -'e' on both sides of the pronoun.

-- 
SuStel
http://trimboli.name