Change financial inventory from Site/Warehouse to Site only
If you have processed any transactions against an item under a given Storage Dimension group, it is no longer possible to change it. You may or may not be able to unravel and delete all the downstream transactions, though it's exceptionally unlikely. You'll need to setup a new item number with the correct Storage Dimension group (configured for Site-only financial inventory), then post an inventory movement journal to reduce your on-hand quantities for the old item and another journal to increase your on-hand quantities for the new one (once your new item is fully established in the operating legal entity). This definitely can become a painful process, especially if your item has a high impact on upstream bills of materials and documentation, but Dynamics does a good job of locking down incompatible changes.