query on stamping with suffixed page numbers

[seanpowell75]

What I'm trying to do is to replace 1 page placeholders in an existing production set with stamped versions, maintaining the original numbering but suffixing in order to maintain page orders on the stamped pdfs. So the 1 page placeholder ABC.001.002.0003 still gets output as ABC.001.002.0003.pdf but will be stamped as ABC.001.002.0003_001, ABC.001.002.0003_002, ABC.001.002.0003_003 etc.

File is outputting correctly using {docid}.pdf in the PDF Export section, however I have tried setting Stamping Right as both:
{docid}{page_3} and {custom_1}{page_3}
where {custom_1} is set to a custom metadata field called "Production ID" which also stores the value of the DocID for that production set. However both options result in the text being stamped rather than the values. ie, its inserting the actual text, not treating these as placeholders and inserting the values.

Is this something you could tweak in the script to allow these to be referenced when stamping? I've been able to use type Metadata and reference CUSTOM:Production ID which gets me halfway there, but not to suffix the page number which is the tricky part.