Title pretty much sums it up. 
I have a website, where custom js file is located, and in order to write some tests, I need to disable loading this js file but inserting my custom js file instead. Using execute_script function from Chromedriver. And here I'm not sure about the working approach.
I was thinking about adding rules in NoScript add-on which will prevent loading of first js file, turning him off and injecting my js file, but I'm not sure whenever it's possible.
Selenium is designed for end to end testing. If you have to alter the content of the page, you are probably using the wrong tool.
It's possible to alter the page with Selenium with a piece of JavaScript via executeScript. However it can only be done once the page is fully loaded and probably after the execution of the original script.
One way would be to use a proxy to intercept the resource and forward a different one.
How to prevent Selenium from loading js file?