Only required if you own Fallout 4 on Steam:

In this case, rolling back to the 1.10.163.0 version of Fallout 4: GOTY Edition is still doable but far more complex. But don’t worry, we got you covered. To do so, follow this instructions:

Type steam://open/console into your browser. This will prompt Steam to open the console.

There, you need to download each part of the previous Fallout 4: GOTY Edition version by typing the following commands into the console:

For Part A use:
download_depot 377160 377161 7497069378349273908

For Part B use:
download_depot 377160 377163 5819088023757897745

For the executable file use:
download_depot 377160 377162 5847529232406005096

For the English version use:
download_depot 377160 377164 2178106366609958945

To download the content for each of the DLCs that you may own type these commands
(having those DLCs is necessary to play Fallout: London):

For HD Texture Pack use:
download_depot 377160 540810 1558929737289295473

For Automatron use:
download_depot 377160 435870 1691678129192680960

For Automatron English language pack use:
download_depot 377160 435871 5106118861901111234

For Wasteland Workshop use:
download_depot 377160 435880 1255562923187931216

For Far Harbor use:
download_depot 377160 435881 1207717296920736193

Far Harbor English language pack use:
download_depot 377160 435882 8482181819175811242

For Contraptions Workshop use:
download_depot 377160 480630 5527412439359349504

For Vault-Tec Workshop use:
download_depot 377160 480631 6588493486198824788

For Vault-Tec Workshop English language pack use:
download_depot 377160 393885 5000262035721758737

For Nuka World use:
download_depot 377160 490650 4873048792354485093

For Nuka World English language pack use:
download_depot 377160 393895 7677765994120765493

These files will download into your Steam library folder
(by default it is “C:\Program Files (x86)\Steam\steamapps\content\app_377160”) in separate depot folders, for example, the Fallout 4 executable file would be in a folder named “depot_377162”.

Once you have these files downloaded, create a new folder on your desktop, and copy the contents of each of the aforementioned folders into this new folder replacing files as you go.

Once you are done, it means you have constructed the entirety of the previous version of
Fallout 4: Game of the Year Edition. Now, simply delete everything in your current
Fallout 4: GOTY Edition installation folder and replace it with everything in this folder.

Once this is complete locate your Steam app manifest file for fallout 4.
The file we need to find is called “appmanifest_377160”. It is typically found in the Steam apps folder E.g:

C:\Program Files (x86)\Steam\steamapps\appmanifest_377160.acf

Right click on the appmanifest_377160.acf and click properties and set the file to read only by ticking the read only tick box. Now press OK.

This will nullify Steam’s ability to update the game automatically by any means unless you accidentally update through Steam forcibly.

Once you have downgraded Fallout 4 and downloaded Fallout: London through GOG,
you can now manually install the mod if you wish to do so.

Some users may wish to do this to add Fallout: London to a mod manager,
allowing them to enable and disable Fallout: London on the fly.

To manually install Fallout: London without the use of the installer,
start by locating where GOG has downloaded the files to:

Inside of this folder you will find the installer, F4SE, the Data folder and more.
Bear in mind you will have to install F4SE one way or another.
You can use the F4SE files included or install it as normal through the Silverlock website.

From here you can zip the Data folder and install the zip as a mod in your preferred mod manager:

We highly recommend you use our INI files that are also included.
You can either replace the INIs in your documents/my games/fallout 4 folder OR
You can add our INIs and their settings to your preferred mod managers INI editor.
These can be found in the _Config folder: