Reasoning behind the construction of nu ... dar: Starting with the word narudar and taking inspiration from how the translation of bid changes in bid ... ibac (from "so" to "as"), something similar could happen for dar when using it with a negated word; thus, nu ... dar. This would explain how narudar (negative particle + ar'u + dar) is not "not an enemy no longer," but "not an enemy temporarily."
This would only go against the double negative as an intensifier if the double negative applies to negative words appearing in any part of the sentence, rather than requiring that, to be used as an intensifier, the negative particle must come in front of another negative word. To offer a solution for how to use dar as "temporarily," I decided to go with the latter. While I think nu dar could have one meaning (such as, "no longer and never will be"), putting a word in the middle of the phrase could cause it to take on different translation ... again, in the same way that bid ... ibac is not translated as its individual components.