I'm not official in any capacity, merely repeating what is stated in the FAQ.
Shadowrun Missions uses all the rules, unless they are marked optional, and even then some specific optional rules are specifically marked as allowed in SRM.
So yes, if you find a rule that is written up as "This is the way things work now", rather than "This is an optional set of rules", it applies in SRM.
Note that books are considered, as noted elsewhere by the campaign coordinator Bull, to be "official" for the campaign when the print copy hits the streets, or in the case of PDF-only product when it goes on sale.
Also, while individual GMs are supposed to try to follow the printed rules and and missions whenever possible, they can alter rules if it's necessary to create better gameplay. Like, if a book rule would make for a stupid illogical situation that is patently un-fun for the game, the GM can alter things to make sense.
-k