Can you use Second-Hand Goods open ability to remove an attachment in your discard pile from the game?
Open: Remove one of your attachments with a base Gold Cost of 4 or more from the game: Draw 2 cards.
Second-Hand Goods, Discard Pile
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.
Can you use Second-Hand Goods open ability to remove an attachment in your discard pile from the game?
No, per In play and out of play: "Cards that are not in play [...] have the following limitations: [...] They may not be used or changed to pay costs."