We accidentally created a Lot Numbered Inventory item and it's on roughly a half a dozen transactions, which are all in closed/locked periods. The item should just be a normal Inventory Item. Is there a way for me to convert the item record? If not, how should I approach modifying the affected transactions in a way that doesn't impact our historical financials? We need to do this so we can turn off the Lot Tracking feature.

Easiest path forward is to create non-lot numbers then adjust off the lot inventory and adjust on the non-lot inventory. You cannot convert items in this manner and if you'd end up deleting and recreating relating transactions.