I have a problem, I want to write a plugin that will edit the page and I can write a plugin, but I don't know how to make a plugin that will edit the page (javascript)
Why reinvent the wheel, just use an extension that injects code.
For example: https://chrome.google.com/webstore/detail/page-manipulator/mdhellggnoabbnnchkeniomkpghbekko?hl=en