What was the name changed on May 14 after Yongzheng acceded to the throne?

Yin Gui was changed to Yun Gui, and all princes were required to change Yin Gui to Yun Gui to avoid the taboo of Yin Zhen in the name of Yongzheng.

Other people who have been ordered to change their names are

Old Eight Yin Zi changed into Azina, and some people think that Old Eight changed this for herself, which means "freezing fish on it" (definitely not a pig or a dog. )

Laojiu's "Yin Ghost" was changed to "Seth Black", which is now generally considered to mean "hate" in Manchu.