Hi Matt,
For example, with the 'header-10' block you're wanting to customize but this block will be overwritten when updating new version of template so you can look for the file of this block:
/templates/ja_blockk/html/layouts/t4/block/header-10.html
just duplicate this file + rename to a new one, something like: header-15.html
Then edit as you wish + change to use this new block in the Layout settings of template.
This new block will not be affected when updating new version of template.
Regards