You can turn an unrestricted 8-way to 4-way by just using a smaller actuator, but the result is a big sloppy mess.
The smaller actuator makes the stick engage farther out from center.
It also makes it so that the stick will have dead spots in the corners, and no guides to force you to the true direction.
A dedicated 4-way, or a true 4/8-way switchable is the way to go.
That will give you the diamond shape to make it feel right, and will allow the stick to engage closer to center, like it should.