What changes does Napoleon make immediately after the expulsion of Snowball?

Napoleon knows that Snowball could conceivably return so all blame is shifted to him. Little by little, everything that has gone wrong-including the re-writing of some of the history in minds of the animals- is blamed on Snowball.

Immediately, the day to day operations change. Perhaps most important is the abolition of the Sunday meetings. The meetings are now only a listing of the week's upcoming duties. Since this is where Snowball and Napoleon argued, the elimination of the meetings will keep another Snowball figure from rising up to challenge Napoleon's power.