AVM offers a friendly user interface with Fritz!OS for their Fritz!Box’es to unleash a nice range of features. Many things are possible, though some things take quite a few clicks.
One of the things that take many clicks, is arranging port fortwarding for hosts on the LAN.
The easiest way, after a fashion, is to make a backup of the configuration, make changes and import the file again. The difficulty here is that the file is checksummed, and Fritz refuses to read the configuration.
While the ages, solutions have been written in various languages. I use a python script, fritzchecksum, written by Mementum/DRe.
It is an pip-installable module,
pip install fritzchecksum, takes a Fritz-file as input and returns the old and new checksum for easy search and replace. The program supports automatic editing of the file as well, I have always replaced by hand.
For future reference, the zip contains the current download from github. Should not be necessary to download it here, but you never know!