Multiple Null/Loopback drivers?

Currently I have one lonely null services driver in my tree that simply changes the password expiration time to midnight.

But I'm going to need to add more functionality for when a user gets created to "extend" the schema class for my new aux class.

So the question(s) I have:

1) Is it better to just enhance my existing null services driver or should I create a separate driver for this purpose?

2) If you have multiple drivers, how does IDM determine which (if any) drivers does its things "First"? Or does it matter?

Thank you