Prior to z/OS 2.1 support ptf RO60393 the CHANGE IF command only worked with logonid BIT fields.
z/OS 2.1 enhancements(ptf RO60393) include changes to TSO ACF command (and ACFBATCH), CHANGE IF processing to allow you to define a GROUP field for all users who do not currently have a GROUP field defined in the logonid. This enhancement allows for the CHANGE IF command to change logonid bit fields or data fields. Prior to this enhancement, CHANGE IF could only be used for BIT fields. Changes to data fields would receive the 'ACF6C030 INVALID OPERAND - field' message.
For example the following CHANGE IF command will change all logonids that have MAXDAYS(60) to MAXDAYS(90):
ACF CHANGE IF(MAXDAYS = 60) MAXDAYS(90)
Details can be found in the CA ACF2 for z/OS Administration Guide r15 in Chapter 3: Maintaining Logonid Records, section 'CHANGE Subcommand'.