Changes Happening Soon to Fallout 4
In case you haven't been following, Bethesda plans to release their "next gen" update of Fallout 4 on April 25. At present we do not know how substantial their changes are going to be, but it's a fair guess that mods will end up broken, as well as a bunch of Wabbajack modlists that depend on them.
Also, on April 30, the Fallout 4 Experiences Wabbajacks by ScreamingLake are being entirely decommissioned and taken offline. These include popular modlists such as Stay FROSTy (FROST list) and Lost World.
First, if you want to keep any of the F4E lists, grab them NOW before they decommission. They will not be available after April 30th! Download them, put them on a drive somewhere, hold on to them. You can find them through the Wabbajack client.
I am also recommending that you prepare for the possibility of a worst case scenario on the F4 next gen update: that it changes a lot, breaks a lot, and there's no easy way to roll back. I hope it's easier than that, but my recent Starfield experience has got me jumpy. You should probably take steps to keep the pre-next gen version of FO4 around for compatibility purposes.
My advice:
Stop Automatic Updating for Fallout 4 in Steam.
In Steam, go to Library, right click on Fallout 4, and select Updates. On the top setting ("Automatic Updates"), change that to "Only update this game when I launch it."
This will prevent Steam from simply installing the update as soon as it can. It will take at least a day or two after release before F4SE is updated, and this way you're not up on blocks while that happens. The game will only be updated when you tell Steam to do it or you start the game directly through the Steam client (which you shouldn't be doing anyway).
Make a Backup Copy of Your Fallout 4 Installation
If you are using Mod Organizer 2 (and if not, WHY NOT?), it's relatively straightforward to make a backup copy of your Fallout 4 installation and then use the backup for playing. This way you can update for next gen, enjoy whatever new features that brings, and then also use the legacy FO4 install for older lists and mod compatibilities.
First, make sure you are doing this with PORTABLE instances of MO2, and that your profiles are set to profile-specific saves and INI files. A regular (i.e., nonportable) MO2 instance uses global system settings and you don't want that for this. Any downloaded Wabbajacks should automatically be using portable instances.
1. Make a complete copy of your Steam FO4 install directory (i.e., Steam\steamapps\common\Fallout 4) and put it somewhere outside of your Steam file tree.
2. Temporarily rename the Steam Fallout 4 directory. It doesn't matter what you rename it to. The point is to make sure that MO2, Steam, etc. can't find the official installation for now, so that if something has gone wrong you'll know it.
3. Boot MO2. Again, make sure you're doing this with portable instances.
MO2 will complain that it can't find the install directory (this is why we did #2), and then will give you a list of possible games for it to manage. Select the last one (custom) and point it to the directory of your FO4 backup.
(Strictly speaking you can also do this in a non-portable instance and using the Instance Manager. Do whatever is easier for you - just get those directories changed.)
4. In MO2, in the upper right, see the executable dropdown. Select "Manage", and go through each of your executables, change their directories to the backup.
5. Start Fallout 4 from the MO2 portable instance and make sure everything works. If not, go back over 2-4 and figure out what you missed.
6. Once you've verified the game is working, go back into the Steam directory, rename the directory back to "Fallout 4".
That should keep you rolling with the legacy Fallout 4 using the Wabbajack of your choice, just in case the next gen release is substantial enough to effectively fork the mod community. Hopefully it won't be, but we cowpokes, we take it as it comes.
I have not tested any of this with the GOG release, but I expect it would be the same process, only without the Steam stuff.
My best,
G.