How to change fritz.box to xyz.box

[joerg-wille]

I have connected 2 Fritz!boxes via VPN and I would like to have separate search domains to solve DNS issues.
So I want one the boxes to use the "fritz1.box" instead "fritz.box". Other than that I actually do not want to change anything at all.
I assume that changing the variable "CONFIG_HOSTNAME=fritz1.box" would do the trick.
I could not find a way to change this variable on the regular Web-IF, nor was I able to modify it using Fritz!Box Tools (downloading, modifying and uploading settings).
I guess I must bake a new firmware using Freetz. What is the easiest way to this? Could not find any patch or similar. Thanks!

[joerg-wille]

I have only searched for duplicates in English.
Well, found the same question in German: #322 "Nur Domainname "fritz.box", nicht mehr..."
But it seems not answered.