The whole Anderson / Udina councilor thing is actually part of one of the books they did.. So it's in extra media that you don't come across if you only play the games.
Something Anderson does basically results in him taking action where a councillor shouldn't... and thus he resigns to not cause trouble, leaving Udina to take his place.
Hm, my theory on the Shroud sabotage is that it relates to the thermal issues - ie, the Salarians had modified it to vary the temperature when expelling whatever organisms were involved - thus any potential genophage cures (which by all that is known would be some form of biologically tailored virus like the original genophage) would therefore be stressed/altered/destroyed so as not to work). In fact, that might have been part of what was slowing down the Reaper poison?
Or if it wasn't slowing down the poison, the Reaper's might have been using some form of nanotech, which would have been immune to those sorts of temperature variations that the sabotage caused....
See, wild speculation abounds..