How to have custom margin for pages containing heading 1

Questions
1

I am creating a report in which 1st level heading is a chapter. It is centred on the page and always starts on a new page. The chapter pages doesnt have headers. I want to have some extra margins in subsequent pages because they contain headers and i want to push them down to prevent them from cut out from final binding process.. Is there someway to set margin based on specific context rule like:

margin: context {
    if is_chapterpage() { 1.2in }
    else { 1.1in }
}
2

I would set a general margin for the normal pages and then a chapter specific margin in a show rule for the chapter heading page.

// general settings
#set page(margin: (top: 1.1in), header: [Some Header])

#show heading.where(level: 1): it => {
  // chapter heading specific
  set page(margin: 1.2in, header: none)
  align(center+horizon, it)
}

= Chapter Heading

#lorem(500)

= Chapter Heading2

#lorem(500)