Hello @openemr-dev - welcome to the OpenEMR community.
Yes, rebranding is fairly common, and plenty OK to do as long as it complies w/ the GPL restrictions per that posted resource.
OpenEMR has several UI customizations that are within the reach of non-developers, particularly in the global configs at (from the main menu) Admin/ Config; the Appearance and Branding tabs. Several other interface mods are found in other tabs lower on that side of the page.
The OpenEMR wiki has limited information on the specific topic of rebranding but you can look here for a search on ‘logo’ which returns some specifics applicable to rebranding:
https://www.open-emr.org/wiki/index.php?title=Special%3ASearch&search=logo&go=Go
Here’s a search on the forum which has some useful perspective and information:
https://community.open-emr.org/search?q=rebrand%20%20order:latest
Good luck with your project- HT