on the other side, WHY?
If it is just an "identity" field, or a variation on the theme of making an artificial field to assure uniqueness of the record, caring about the increment (of even type/character) is just a waste of resources.
I'm sure that you have a handy (and dandy) rationale for the 'requirement'. but think about it for a bit before re-inventing the process.
OBTW, your uniqueness gets to be a lot more of a chore when you have multiple users in the db, and that is more worthy of the attention.
MichaelRed