which BGP feature allows a BGP router to act as a router within one autonomous system to some BGP neighbors but also appear to be in another autonomous system to other neighbors?

During the autonomous system number migration process, which BGP feature allows a BGP router to act as a router within one autonomous system to some BGP neighbors but also appear to be in another autonomous system to other neighbors?

A.
remove-private-as

B.
local-as

C.
as-path prepending

D.
AS override

E.
Site-of-Origin (S00)