Yes but not as easily as you do now with your two April contracts. If you purchase a contract with a different Use Year, it will not be added on to your current membership. MS will create a new membership for you and add the new contract under that new membership. You have two options for "combining" points from two different memberships.
1. You can transfer points from one membership to the other and use them as one pool of points to make a reservation at 11 months out if all of the points are from the same resort or at 7 months if the points are from two different resorts. You cannot see transferred points online unless they are for the same resort and UY as one of your own contracts so you will not be able to make a reservation online with those transferred points, you will have to call MS.
2. You can book your stay as two reservations, booking the initial nights of your stay under one membership and the rest of the nights under the other membership. Provided both reservations are for the same resort, room size and booking category, MS can link the two reservations to alert the room assigner to put you in the same room for your entire stay so that you won't have to change rooms. You may have to check in/check out on your transition day however.