Margin Control per Page

Hello there,

I know you can change the margin for every page by editing the setup file
then @Include them in the document. But is it possible to change the margin
for any arbitrary page?

My hack was to setup the smallest overall margin, then wrap the content
after @NP (new page) with a larger margined @Box. However I realise that
long content inside the box cannot flow to the next page.

Thanks for the help,
Robin