rhcomputer:

1. Grasshopper is the rank on the site; the username is metawizard2 😀

2. Other way around:

What is common among the user records that you can hook on?

In your first post you said that you have internal users with scheme:

12345

and external users with scheme

TS-3456

So, lets take an actual user, Bob Noodle.

Bob is an internal employee with ID 12345. He is also an extrnal employee with ID TS-34567.

Is that a good representation?