mass change GL accounting flexfield values

we are public sector entity and our chart of accounts is prescribed by the state.  the state is now changing the numbers used in 2 of the GL accounting key flexfield segments.  This will require us to change many segment values and potentially lose historical comparability.  is there a way to change flexfield values other than manually changing each one?  also is there a way to set up a crosswalk in the GL to facilitate trending with old data and provide users with new account lookups?

oracle apps version 12.1.3

any assistance will be greatly appreciated

thanks