There could an option for adding a same piece of code for all pages, i.e. for the code i use for removing the “add picture” picture from galleries. Right now the only way is to manually move to and insert on each page separately.

You can use the Stylish extension for Firefox to do this, or a custom stylesheet in Safari. If you’re using another browser, there’s probably a way to specify a custom stylesheet, too.

Yep, but that fixes the outlay only for myself, each other user having to do the same, which in our case they don’t necessarily don’t have interest in or skill to do.