They can introduce new types of questions without warning. They have done it in the past. Befor umat used to have t qs like how many squares are in the figure and then one yr they randomly changed it to sequence questions without warning.change in difficulty? of course. one can speculate that s1 will be made easier/passages shorter and that s3 will be harder, but at the end of the day its up to them.
change in question type? no, unless they specifically state it or change types of sample questions in their booklets.
if u read their booklet for 2009, it will all be in there. e.g. no. questions, time limit, sample questions etc. they will not mislead you into thinking the umat is one type of test when it is completely different.