I just wanted to run it past the modder's to their recommendation on the optimum way to add new spell tomes while maintaining maximum compatibility.

My Oblivion modding instincts tell me that I should use a one-time quest and have that "inject" the new spell tomes into the appropriate levelled lists so they appear on the right vendors without actually changing the levelled lists directly (In same way I'd "inject" the spells onto the vendors in Oblivion); is this how I'd handle it in skyrim or would this be over-thinking the problem and we now have new tools at our disposal (Skyrim spells are objects rather than spells from an acquisition point of view so... couldn't I just add a new merchant container?)