Hello Ken-

No, the Modify Static button doesn't appear when you're only connected to Prime. It only works for Legacy.
As far as I can tell there is no Prime integration to the Pi-Star dashboard yet, though it should be possible in theory since Selfcare exists.

I have not yet tried to send commands to the hotspot while tethered to a phone, though I have seen several places that it's common not to work so I wouldn't be surprised if you couldn't do it.

It's probably not worth all the time necessary to build all the channels since it sounds like the switch-over is close.

73,
 -Brian