Add and change footer and header for all or part of mail templates

Good day,

I am relatively new to One Identity Manager, Designer, etc..
I have already searched in the forum and via Google, but did not find a suitable answer.

Is there a way to add a new footer and header to all or part of mail templates at the same time or does it have to be done for each mail template individually?

Many thanks in advance and best regards,
Florian