I have created a template (.dot) with the page layout: 210,00 mm width
and 120,00 height (Portrait).

Is there any easy way to change the Page length for a given page in a
document or do I have to use Section breaks?

I would like to write a certain amount of information about a subject -
on a given page and therefore not have the current page length longer
than necessary.

Any ideas ?

Regards
Rune.