That’s the first time I’ve ever come across the phrase “imperfected tensed forms”, but it’s pretty clear it just means forms in the imperfect tense, isn’t it?
I mean, I probably would have written (had I been inclined to write it at all!) “disallow forms of bod in the imperfect tense…”, but is the other form used really comparatively that opaque?
And as for “…in affirmative and declarative contexts, embedded clauses cannot contain the present tense of bod…”,
Surely that is an effective and concise way of saying it, if the words within it have been defined?