How to replace part of the code in a page in real time?

Question

Browsers

You need to change the code on one page. Like how you can make a debugger through Chrome, but only so that it always works (including when updating). How to do it?

Answer 1

Look towards tampermonkey for Chrome or greasemonkey for Firefox.
Then you create a userscript from your code and set a condition to run on page load.