In reviewing the ACF2 Message manual, shows this reason from ACF00112:
Reason: The field you want to modify (fld) is marked with a RESTRICT flag. Only an unrestricted security administrator is authorized to modify this field.
The ACF2 manual under
@CFDE shows this for FLAGS=RESTRICT:
RESTRICT—Only unrestricted security administrators can change this field. This means users with the SECURITY privilege and no SCPLIST restrictions specified in their logonid records.
The default shipping of the ACFFDR for PREFIX has this:
@CFDE PREFIX,LIDPFX,CHAR,ALTER=SECURITY,LIST=ALL,
FLAGS=RESTRICT,PRTN=9,RRTN=1,GROUP=11
If the scoped Security Admin needs to change that field, then FLAGS=RESTRICT must be removed from the ACFFDR using the UM99901 usermod.