We do grow limbs routinely, in utero. Typically 4 limbs per person. I would assume that we would be looking to activate the genes responsible for that same process. You can look up timelapse videos of embryos on youtube to answer your question.

It seems more likely for there to be a single set of genes responsible for growing a limb than 2 sets in the Axolotl. Especially since the new limbs seem identical to the old ones, rather than following a distinct backup blueprint.