You can't - its part of the code.
In Netbackup 7.6 you can choose "Orphan Snapshot Handling" in the VMware policy under "VMware" tab to either "Ignore" , "Abort" or "Removbe Netbackup".
Remove Netbackup meaning, Netbackup will remove its own orphan snapshots.
I agree with Nicolai - the only snapshot parameter that can be changed is Snapshot retry count.
Best to find reason for failure to remove snapshot - user rights is normally one of the reasons....
In VMware Advanced Attributes (Extract from NBU for VMware Guide):
Snapshot retry count :
Sets the number of times the snapshot is retried. The default is 10. The range is 0 to 100.
This option and the snapshot timeout and snapshot creation interval provide flexibility in the
creation of snapshots. For most environments, the default values are usually best. In special
circumstances, it may be helpful to adjust these settings. Example considerations are the size
of the virtual machine and the processing load on the VMware server.
