Is it possible to update the multi-warehouse support module (as of yesterday packaged with Magento 2.3) if you already have Magento 2.3 installed from before MSI 1.1 was included (in particular with Magento having been installed via GUI and not composer)?
I just went thru that, the answer is no. However, even after re-installing (with composer), using latest magento 2.3, InventoryApi only shows as version 1.0.4. Composer is showing that as the latest available version. However my previous install showed 1.0.3. Confused.
Actually, i thought i read it wasn't possible, but when asking my hosting provider for support running composer due to out of memory errors, they ran the update command under my old instance that i installed without composer and it looks like it updated. Which is weird because i swear i read on the magento site that you need to install with composer to upgrade modules.
I'd give it a try.