The theming guide I linked in the other thread shows how to create child themes.
You could basically create a child theme of the bootstrap theme and only add the modifications you need to your child theme (in this case the modified template file and the custom data to be passed to that template).
So I suggest that you start by reading the guide, at least about child themes and then about passing custom data to templates. There is a whole section titled “Child Theming the Bootstrap3 Theme” and “Passing Data to a Single Template”.
I am sure that you could achieve this also by editing the core and of course you could apply your changes after each upgrade.