Assume the current user has an Access Level of 'Staff'
READ PROTECT Invoice.Amt FROM ALL EXCEPT System AND 'Staff'
... will restore access to 'Staff'
Problem is, thats not Dynamic, its hardcoded.
You cannot do this:
READ PROTECT Invoice.Amt FROM ALL EXCEPT System AND LoggedInRegularUser.AccessLevel
So, maybe
LoggedInRegularUser.tmp_string = 'READ PROTECT Invoice.Amt FROM ALL EXCEPT System AND ' + LoggedInRegularUser.AccessLevel
EXEC_STRING LoggedInRegularUser.tmp_string