I think you might be right. My source was Gardyne's history of the Gordon Highlanders. It does sound like it could have been a reminder to regiments going on active service what the current regulations were.
The 92nd had been in the Peninsula since Aug 1808, so the order seems a bit late for them as an instruction for going on active. I don't have the book to hand to check the context & I wonder whether I have I have noted the date correctly.