I had a similar situation and used a login-type procedure when the workbook was opened - with a different password for different levels of access. The status of the logged-on person was then recorded into a 'veryhidden' sheet (could also be written to the registry). You could then use this to disable whatever macros you wish - and even place an open event into the other file(s) so they make sure they are only opened when the main workbook is open and by the correct level of person
I actually hid various buttons dependant upon who logged on - so the user would not even be tempted !