So as it stands right now on live, and this has been the case since the PTR,
- the change to the Succubus spell making it the Sayaad spell permanently made your succubus whatever it was prior to this patch.
You CANNOT use the vanishing dust on the spell anymore, because the system does not mark it as “glyphed” anymore.
You CAN use a glyph on the Summon Sayaad spell and it does change the Succubus to whatever the glyph is, but this change becomes permanent and you cannot return the succubus to her original form.
Likewise, there is no option to make the Summon Sayaad spell “random” again if you choose one or the other.
Once you pick an option, you can only change back to the other summon (ie switch between permanent succubus and permanent incubus).
It would be nice to have a third option “I would like to summon either form randomly again”.