You can obtain certain FH1 DLC codes via eBay (pre-order cars are an example); and I can confirm that all three of the Limited Collector's Edition codes (Day One DLC and 5 custom liveries, VIP, and 3 tokens (the last of which must be redeemed on an Xbox 360, NOT via BC on an Xbox One)) are functional as of the date of this post. While you cannot purchase anything from the in-game or Xbox Live Marketplaces, unused codes DO seem to still be working.