Can I change a non-reusable Sequence Generator transformation to make it reusable?
You cannot make the transformation reusable, but you can change the transformation to use a sequence data object. The sequence data object maintains the integrity of the sequence, regardless of the number of transformations that use it.
Can I place a non-reusable Sequence Generator transformation in a mapplet?
No, you cannot. Mapplets are reusable objects, so all objects in the mapplet must also be reusable. Use a reusable Sequence Generator transformation instead.