@ PondusOki ;)
It isn't that it is OK or not, I think this url is just used as an example, the OP is looking for a means of changing the default text.
@ yurikashanako
Since these Blocked URLs are either user based, e.g. the user or administrator blocked then if you aren't that user or Admin (even if a method is there) then you wouldn't be able to.
What environment are we talking about here, Home or Business ?
You posted in the General forum and not a forum related to the environment it is used, e.g. Avast! Business Protection forum or Avast! Free/Pro/Suite.
There is a Blocked.htm file in the C:\Documents and Settings\All Users\Application Data\AVAST Software\Avast\HtmlData or C:\ProgramData\AVAST Software\Avast\HtmlData folder depending on OS. Now that unfortunately doesn't have that boiler plate text, just a reference to %_TXT% so I don't know where that parameter is imported from I couldn't find it.
As Scott mentions even if you were able to do this it may be restored on a program update or integrity check.
@ Pondus
It isn't that it is OK or not, I think this url is just used as an example, the OP is looking for a means of changing the default text.
Access to C:\Documents and Settings\All Users\Application Data\AVAST Software\Avast\HtmlData\Blocked.htm was denied
You're welcome.
Generally topics remain open, in the forums, they just fade away over time they drop of the chronological listings, unless retrieved on a forum search.