Injection body + head in which file are those made

Injection body + head in which file are those made

I know that i can make them in the basic settings, but in which files can i enter those changes manually? Thank you

You would make them in the template files.  The only thing is that you might want to copy the template into a new one so that future updates don't overwrite your changes or just made notes that you changed the files so that if you upgrade in the future you can add your changes back after the upgrade.