Hi,

yes, you can download the odoo add-on code from the GitHub repository. And you can make changes in the needed template by inheriting them.
Please go through the below Github repository

https://github.com/odoo/odoo

Note: You can change the branch of repository according to the version you need.

Hope it helps

I'm unable to send you a link, but if you highlight a chunk of text, you'll see a popup with an option ">" (hopefully that doesn't get stripped). if you click on that icon (should be on the far-right), you'll see a popup with all the html. Copy/paste that into an IDE and you're good to go!