Hi Audisho,
I'm not the original author of this post, but this is related to a problem I am having.
I am not able to do any screen level edits. When I do change the default screen, the murl link will no longer work. I get an error that I do not have permission to view the page.
I brought this up several months ago here in the form and was told that this was a known issue and was to be fixed. It appears that it has not been.
For all intensive purposes, a web-to-lead form that can not be customized is almost useless.