Some games allow balance adjustments to be made without issuing a title update or patch. Monday Night Combat is one example of this (Source). This is especially desirable on Xbox 360, because the certification process for title updates can take months and cost developers a large sum of money.
This thread on BSN lists the balance changes that are slated for Mass Effect 3 multiplayer. Will these balance changes take place behind the scenes (immediately), or will they only occur after a title update or patch is issued?
It seems to me like the easiest way to know for sure would be for an Xbox 360 player with a Quarian Infiltrator to test whether the Sabotage changes have taken place already. I would test this myself but I haven't unlocked that race yet.