Do something when setting a type parameter?

Try this then,

Type Sprite
	Method Order:Int(NewValue:Int=-1)
		Global value:Int
		If NewValue <> -1 Then value = NewValue 
		Return value
    End Method
End Type

ThisSprite:Sprite = New Sprite 
ThisSprite.Order(10)

A = ThisSprite.Order()
Print A

A = ThisSprite.Order()
Print A

ThisSprite.Order(0)
A = ThisSprite.Order()
Print A