XenForo 2.0 – removal of copyright | NulledTeam UnderGround

Can anyone respond?

I want edit copyright text of Void to XenForo ™ Forum Software © 2010-2018 XenForo Ltd.
If I do this on file xf.php, on line 735 will begin to show error in the administration.

I want a copyright text that I do not want to deactivate, I just want to edit it.

I ask how do I disable this error message, I really do not like it. Can someone help? I can pay for that.

After doing this edition I see every time in the administration this: