Hey guys, I'm new here, this might be a dumb question, but I want to know can we override or modify site builder backend files (js/ts) as we can do in SuiteCommerce Advance?

Hello, There are 2 areas in SB... the 'main' section that is on the shopping domain and you can't modify the back-end scripts there but you can change the theme and basically do whatever you like, even commenting out the base code that NS sticks in there. for checkout & my account, the version SB comes with has very little customization that can be done, but you can install the Kilimanjaro site builder extension and update it... it's based on SCA (years old, and NS will never again update it).