I've never studied ME either, but it seems to me that your line 27 might be a slightly free translation of the more literal ".... you might feed (yourself) thereon your fill."

The ME on-line dictionary I looked at didn't show equivalents for "lythly" or "sekyrly", but on analogy with "loath" and "secure" I would suggest "reluctantly" and "surely".

Line 31 - there is no "not" in the original. ("Or else we may be blamed, I'm sorry to say.")

Line 40 - a boon is a favour.

Line 44 - rather a nit-pick, but to the author, "God and the Trinity" would have been a very different and probably heretical phrase compared to "God in Trinity".

Line 48 is surely simply "He is helping us now in our (time of) need", because the unborn Jesus is magically making the branch bend.

These are just suggestions - you should check it out with an expert if you have any doubts.

As to why Childs published the original, another reason is that it preserves the true scansion.