I believe there was a ruling about this but my search-fu is weak, so I apologize.
Are you allowed to bow Holdings and produce Gold when attaching a 0GC attachment?
Paying for 0GC Attachments
A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
I believe there was a ruling about this but my search-fu is weak, so I apologize.
Are you allowed to bow Holdings and produce Gold when attaching a 0GC attachment?
Yes. The Equip action has a variable gold cost, for which you may choose to pay 0g (if you have a 0GC attachment in hand), and while doing so you may generate gold.