Yes, you can transfer a grant as long as the transfer is explained and justified and the transfer has received the approval of the ERC Executive Agency (ERCEA).
Possible reasons can be an appointment to another institution or non-compliance of the current institution concerning contractual promises. The new host institution should be able to provide similar conditions to ensure the project remains feasible. The total budget cannot be modified.
The former host institution is required to forward the remaining funds to the new host institution.