OK Ben,
I accept you are responding to what you are referring to there. Namely, the actual Hebrew, without Sean's suggested infinitives. And, as a regulativist, I completely agree that to deviate from the dictate is to (essentially) disobey a command: specifically the command not to add to the word of this law. And as this passage indicates, pragmatism is no justification. The RPW doesn't stand or fall on this passage, but inserting the infinitive weakens an otherwise powerful argument from this passage. We shouldn't have to give up such a strong affirmative passage as this on the RPW on the basis of a weakened translation, I think you'd agree.
Saying that, now I don't believe you'd accept the Heb.: LO'="Do not" in quotes, as not being a strained interpretation, or belonging to an unexpressed infinitive as being equally probative to negating the verbal idea. Surely that's arguing from what's not present, rather than from what is, clearly much weaker suppositions, and not to be preferred. I think you'll agree with this assessment as well.
What you've quoted there from Sean is truncated from Sean's two suggestions. He includes the infinitive "to do" in both, as if either case were a possible implication of the sentence. And I'm arguing that in no case is interpolating the infinitive an acceptable translational gloss. In the first case, you have a gloss that parallels the text, and restates the text. It is acceptable as an interpretation of the text (but not a translation). REASON: because the interpolated "to do" in that case is not attached to the "not" but to the "which"; that gloss can read: "which thing [to do] he did not command them." See, I've just move his "to do" to the other end of the sentence, where it still has reference to the verbal idea in the previous clause.
But absolutely not in the second case. There, again, this "to do" is being attached to the "not". So, no, it isn't normal Hebrew syntax to so read. But as you leave it off, then yes, you can put the "not" at the end of the sentence. You just need to still attach it to the verb, and not put it in quotes, i.e., which he commanded them: "not" (or: which "not" he commanded them); uh-uh, that is practically unsupportable. I'd want to see some other such "substantive-uses" of the negative particle Lo'.
But again, I was dealing with Sean's glosses that include an interpolated infinitive "to do", and not as you were: simply with the text, minus the [supplied] infinitive. Are we in agreement?
[Edited on 6-3-2006 by Contra_Mundum]