There should be no need to realign the dish unless the extreme areas of the tracking arc are out
You should first check there is enough room behind the dish to install the new actuator (It will be up to six inches further back, which may hit a wall/chimney)
Then will the dish be able to move the further distances East or West ? Not just the limits of the reflector (again it might hit other objects) but the bearings in the polarmount - Lenson Heath dishes for example are limited to 45 degrees either side of South
Replacing the actuator for one of the same shaft diameter is straightforward, if the original joint on the back part of the dish is uncorroded then reuse it
Set the mechanical limits up correctly when its all done, the receiver should be able to reset ther electronic limits without difficulty