I never said the ESDs gave me a forbidden error, I was referring to the ISO. The reason the update assistant wouldn't download the ESD file for me was because the URL it was accessing to get the products.xml file was giving a response the tool wasn't expecting. I simply used Fiddler to trick it into downloading the correct products.xml, and it was able to download the ESD file and upgrade just fine. In fact I just finished the upgrade to 15063 just now using the upgrade tool.
I didn't alter products.xml, I used Fiddler to make it download products.xml from gwx.windows.com/preview/cxe/vanilla/products_rs2.xml instead of download.microsoft.com/download/0/4/7/047889D0-578C-4A44-A38F-7F30A6CB3809/current-version/products201682.xml which is where the go.microsoft.com/fwlink/?LinkID=844074 URL redirects to. The reason I found out about products_rs2.xml was because go.microsoft.com/fwlink/?LinkID=844074 briefly redirected there the second time I ran the upgrade tool. I guess I got lucky.
Also, in case it wasn't clear in my screenshots, I had to enable stream mode in Fiddler (stream button on the top toolbar) because the default mode would cause it to only download 2GB and then never complete, with Fiddler eating up a bunch of memory.
original iso = Pro + Home converted esd = Pro + Home + Education (+ Single Language) different containers, same data
Does anyone know how to remove the Mixed Reality Portal and Windows Defender Security Center apps, as well as disabling Windows Defender for good (I guess that if you remove the Windows Defender Security Center Windows Defender will be disabled for good)? EDIT: It looks like it also adds Windows Media Player to the Start Menu and Paint 3D apps. I succesfully removed Windows Media Playe in Windows Features through Control Panel and Paint 3D with the help of CCleaner. It looks like it didn't install all the other apps I had removed in the previous version (1607), which is good and unfortunately only happens now. Also, for those who do a clean install it doesn't install Paint 3D but for those who install it through an update install it does, which is strange.