Code blocks on the forum should now have a Copy button at the top-right, which you can click to quickly copy the whole block into the clipboard.
Screenshot, in case it isn't showing up right for you:
Live version to test with:
@nodeselect
filetype new .txt newname "norename:{file|noext}.txt"
Tested with Chrome, IE and Edge.
(IE shows a misleading warning message implying that the site will be able to read your clipboard if you allow it access, even though it will only set the clipboard. The other browsers don't do that as they seem more intelligent.)