You can use defaults in the page types section of dashboard to do just that. The only downer is if you have a lot of page types you'll have to apply the change to each one. With the scrapbook this isn't the end of the world, but its a thing.

On this site, we've hacked the template files to look for a specific block we made on the home page for the hot spots nav. First made the block, then just implicitly referenced it... works okay..

in the future, we're going to have a "reusable blocks" section in the dashboard that basically gives you a spot to camp these blocks you might use this way.. the downer with the defaults approach is only admin user can get in there... so the reusable blocks approach would be somehting you could tie to regular permissions

so if I edit the page type defaults later on down the road, it will populate to all of those pages that use that page type?

yes, if you make a block in defaults, and change it later, everywhere that block showed up throughout the site will reflect that change.

A semi-related note: if you make a block in defaults, it will only add it to new pages made following that page type. If you want to apply that block to all existing pages you should click the block while in edit mode on defaults and you'll see an extra little option called "setup on child pages"