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.
A player, 7 May 2008
If I have a follower that has an action that states "Battle: Bow this card: Destroy an Attachment" Can I pay gold as an added cost for this action if I want to?
did a cursory search on the rules, tons of stuff that has the words "gold cost"
found this on the wiki which doesn't really answer it: ->It is permitted to overpay a Gold cost by any amount, including producing Gold to pay a Gold cost of zero on (for example) an Action card. It is not permitted to pay a Gold cost for a card with no Gold cost at all.
Thanks
Alex Jones (rules official), 7 May 2008
If I have a follower that has an action that states "Battle: Bow this card: Destroy an Attachment" Can I pay gold as an added cost for this action if I want to?
did a cursory search on the rules, tons of stuff that has the words "gold cost"
found this on the wiki which doesn't really answer it: ->It is permitted to overpay a Gold cost by any amount, including producing Gold to pay a Gold cost of zero on (for example) an Action card. It is not permitted to pay a Gold cost for a card with no Gold cost at all.
Thanks
All action cards have a gold cost, mostly 0 - so you're not paying "an added cost". You may spend any amount of gold, and as long as it's equal to or greater than the required amount, you've paid that cost.
By contrast, abilities on personalities, etc, have no gold cost (typically), rather than a gold cost of 0: if you tried to pay gold for that it would be an added cost, which - as described by the paragraph you quote - isn't legal.
Roger Giner-Sorolla (rules official), 8 May 2008
Also, the wiki you quote goes on to answer your question:
It is not permitted to pay a Gold cost for a card with no Gold cost at all, or for an action on a non-Action card (e.g., Personality, Follower) with no Gold cost.
Zen Faulkes (rules official), 8 May 2008
In fairness, the wiki section mentioned above was adjusted in response to this question. So don't worry if you looked earlier and didn't see it.