Local overrides in chrome – keep active while devt

问题:

I really like the local overrides feature in chrome. While it is handy during development, I'd also like to use it while my devtools are closed. If this were possible, it could replace extensions which inject custom css or js into the page. (right now, after loading a page, overrides do not kick in until devtools have been opened at least once)

After some digging, I got the impression it's not possible though. Can somebody please confirm this? Is there any way to achieve the desired effect (custom js & css) without extensions?