hedit

       images = <object>.ms.imh  images to be edited
       fields = REFSPEC1         fields to be edited
        value = <arcspec>.ms.imh value expression
         (add = yes)             add rather than edit fields
      (delete = no)              delete rather than edit fields
      (verify = no)              verify each edit operation
        (show = yes)             print record of each edit operation
      (update = yes)             enable updating of the image header
        (mode = "ql")           

In practice:

To avoid the tedium of editing each header individually, you can make
a little script. Each line in the script should contain the command that
you would type on the command line, as shown in the example below.

hedit <object1>.ms.imh REFSPEC1="<arcspec1>.ms.imh" add+ ver- show+
hedit <object2>.ms.imh REFSPEC1="<arcspec2>.ms.imh" add+ ver- show+
hedit <object3>.ms.imh REFSPEC1="<arcspec3>.ms.imh" add+ ver- show+
hedit <object4>.ms.imh REFSPEC1="<arcspec4>.ms.imh" add+ ver- show+

Note the use of quotes in the assignment of REFSPEC1. The script can
be executed by typing cl < scriptfile on the command line.