Changing Header scroll height for Twenty Seventeen theme on ALL pages

from that question you mentioned, this is the code:

.twentyseventeen-front-page.has-header-image .custom-header-media,
.twentyseventeen-front-page.has-header-video .custom-header-media,
.home.blog.has-header-image .custom-header-media,
.home.blog.has-header-video .custom-header-media {
  height: 1200px;
  height: 100vh;
  max-height: 100%;
  overflow: hidden;
}

Revision:
Try removing home and front-page from the selectors for your specific use:
You can use this to replace what you put in and it will cover the front page as well.

.has-header-image .custom-header-media, blog.has-header-image .custom-header-media {
    height: 1200px;
    height: 70vh;
    max-height: 100%;
    overflow: hidden;
}

.has-header-image .custom-header {
    display: table;
    height: 300px;
    width: 100%;
}