have you checked your root tclprocs directory? I think Cloverleaf comes with some generic tps and xlt procs (e.g. tpsForceHl7Field, xltStringToLower) that might help.
Putting it on a translate would be way more work since I’d have to have a separate xlate for HL7 A17, A08 and A45 messages because the message structure is different for each.
Having the pre-proc will null out the subfield for each instance of the segment in a message without me having to create separate xlates.