Where I work there is a practice of adding a t_
prefix to all temporary employees logins (sAMAccountName).
When someone switches from temp to perm or the the other way the prefix is add/removed.
While is ok with Windows and AD, this practice is messing most (if not all) other systems that are relying on AD/LDAP for authentication, as they are not able to detect a renamed account.
Is there any strong reason for having such a practice, aren't other alternatives that would play better with other systems?
No, it doesn't.
Don't overload any Name fields with other purposes. A name is supposed to identify an individual. You don't try to stuff their company, department, or payroll info into the name field.
Use an OU, a group membership, or one of the extensionAttribute* fields to indicate temp-vs-perm status.
It seems that you have already experienced the consequences of why your current practice of using the naming convention to distinguish between temporary and permanent employees isn't that well thought out.
I've found that often the temporary employee has the same responsibilities and restrictions as a permanent employee in the same role and only real technical differences between the two you might want to implement in their AD accounts are:
You may also have business requirement to have multiple flavours of an all-staff mailinglist for company-wide announcements (e.g. one for everyone, one excluding temps and one only for the temps) and should be able to manage that and other business requirements with groups.