We recommended that all versions of a single mailing are based on the same template. However , there are some exceptions.
If, for example, you have to produce an English version of a mailing and an Arabic version, then you would have to use a different  template for the Arabic version. This is because the Arabic language runs from right to left and so it has to use its own template. 

If you have a more  complex need to use different templates for versions of the same mailing, then please contact us to discuss.