Can it be screwed on to plate where other seat was?
While this seat's plate appears to be removable, the backrest is welded to the plate, so if you removed the plate, you would lose the backrest. The plate includes a seat post mount/bracket, so you would not be able to mount the plate to another plate as the seat post mount would get in the way. However, if your unit has a standard 7/8" seat post, this seat would fit perfectly on that post and you would not need to perform any plate alterations/modifications.