https://wiki.mozilla.org/Add-ons/Extension_Signing claims that 46 beta
will not have the override. I'm running 46.0b1 and the override still
works.
Is there a more current schedule somewhere?
Note that this it becoming more of a PITA, particularly since in
parallel with signing, firefox is removing deprecated javascript in
stages, thus breaking some addons repeatedly. The breakage tends to
become apparent at beta time. I'm running an unsigned fix to one right
now waiting for the developer to make and sign a final fix.