XF 2.1 Files with unexpected contents issue

[Nysotia]

I'm having this problem since I replace some of the logo icons in xenforo default style. Can anyone tell me how to get rid of the error log. It's just annoying.
I know that It doesn't affect my site, but when I log-in to my admin cp it doesn't look good. The same thing happens when I modify files of any add-ons.

 

[Paul B]

Replace the original files.

Upload your own files to a different directory and update the style properties related to them.

 

[Nysotia]

Replace the original files.

Upload your own files to a different directory and update the style properties related to them.

Thank you Brogan for the reply. It also happens when I edit files in xenforo folders. In addition to any modification to any add-on as well. Do I need to repack the add-on or something? I'm really new to Xenforo. I want to learn more how Xenforo works, so I can build my own Add-ons in the future.
Many thanks.

 

[Paul B]

If you edit or change files that message will be displayed.

You need to extend the code correctly if you want to change the functionality, by creating an add-on.