I don't think you can using official Netbackup tools - It is possible to edit the image header files as they are ASCII, but it's strictly unsupported .
As a workaround : When searching the catalog use the retention level instead of the schedule name - It will give you the same result.
USAGE: bpimagelist [-media] [-l|-L|-U|-idonly] [-tape]
[-d mm/dd/yyyy HH:MM:SS] [-e mm/dd/yyyy HH:MM:SS] [-hoursago hours]
[-keyword "keyword phrase"]
[-client client_name] [-server server_name]
[-backupid backup_id] [ [-option option_name] ... ]
[-policy policy_name] [-pt policy_type]
[
-rl retention_level]
[-sl sched_label] [-st sched_type]
[-class_id data_classification_id_guid] [-stl_complete]
[-stl_incomplete] [-stl_name storage_service_name]
[-M master_server...] [-v]