Use machine names in stead of labels in templates.
I recently updated a Payment gateway Display name (label) and now all my conditional stuff in email templates needs to be updated too. Where before I had "Paypal / Creditcard" I now have "Paypal" which will break all conditionals.
Please change future versions of WHMCS to use internally fixed machine names and externally readable labels. The fixed machine names should then be used for template conditionals, which will no longer break when Labels are changed. Also future translation feature of these labels would not affect template conditionals because these would remain based on the machine names, not on the translation that humans read.