Johnny, thanks.
First I looked for the reg key you mentioned. There was no WindowsSelfHost key - so I searched the entire registry - still no joy. I tried the reg update provided at the Ten site and accepted UAC as mentioned by another poster. No joy. I checked to see if the Insider service was running. It was on manual, triggered, so for kicks I set it to automatic. No change.
The problem I'm having is that the options to change are greyed out. I use custom colors, so you'll see the Dev section is checked in black. The other two are nonselectable ie: greyed out. You can click there but the buttons are not selectable.
I've been an Insider since shortly after Win10 shipped. If anyone has any thoughts on this let me know. I'm considering leaving the program which I'd prefer not to do.