Previously, we used an option to allow duplicate templates, if that
option was passed, we would always replace the existing template with
the new template, and if it wasn't, we would always throw an error even
if the template's content was the same.
Allowing to replace a template with a different one is problematic, as
it may or may not have already been compiled, which may cause various
problems. On the other hand, if the template is the same, there is no
point in throwing an error, as we can just silently ignore the second
addition.
Samuel Degueldre