Verifying Whether Account Is in Use Before Running Script

I'm developing a database in FM 9 Advanced that will be hosted on an
FM Server in a mostly Windows environment with some remote Mac login.
I've scripted an account management section for the database
administrator that allows him to change account names, passwords and
access privileges (as well as other company-specific information) via
layouts and buttons that are in keeping with the rest of the
database's interface rather than having him work with FM's interface
via the File>Manage>Accounts & Privileges menu.

However, since this is a hosted multi-user solution, I'm not sure what
problems he'd run into trying to change an account name or password
for an account that's actively being used. Is there an error
equivalent to 301 (record in use by another) that states when an
account is in use? I couldn't find one in the error list in FM's help
guide. And is there a way to detect, before a script starts piling up
errors, whether a user is using his/her account? I thought maybe a
Get or Design function might exist for that, but I didn't see it.

It seems like the best thing would be to have the script check whether
an account is being used before trying to make changes, and to check
again for errors at he end in case the user logged on while the script
was running. Any recommendations in this area would be greatly
appreciated.

-S.