Would an officer (SS) promoted from Division to Corps CO keep the cuff title from his former div? (Like in the US, a soldier having seen combat with one division is allowed to wear that div. patch on the right sleeve id transferred to another Div.)

In a word - yes. There are many photos of ex-Leibstandarte personnel wearing the Adolf Hitler cufftitle after they had been posted, particularly if their new unit didn't have a cuff title. Likewise "Das Reich", "Totenkopf" etc.

Thanks. Working on a Befhelspanther from 5th SS with TC, officer from Germania PzGren, and Corps commander having a pow-wow on the tank. Pz. Corp commander had been 5th SS's commander. I have Germania cuff titles. Would the Panzer Ggrenadier Regt have used them or were those for early war when the Waffen SS was in it's developmental phase?

Yes. Germania was part of Wiking. It was transferred over from Das Reich. Germania titles are frequently seen in photos as it was one of the original four regiments that started the Waffen SS so it wouldn't be impossible to see it worn by a member of the Corps staff and very likely by a 9 SS Panzergrenadierregiment member.