I am at a point now where I need to create a compatibility patch for my mod to work with the 2 big overhaul mods, SkyRe and Requiem. I've made some edits to some Magic Effects in the game that I want to add on top of the already edited Magic Effects in the overhaul mods.

How exactly do I accomplish this? I tried making a new empty .esp and loading it as active, together with my mod + the overhaul mod, but the CK just tells me "Multiple master files selected for load. Load operation aborted".

Add bAllowMultipleMasterLoads=1 under [General] in SkyrimEditor.ini in your Skyrim folder, this will allow you to circumvent that warning.

Ah, I had already added the DLC bsas to the archive lists but I had forgotten to add that line... Cheers, it loaded now.

Now I'm just a bit confused on what has happened and what I need to do after loading all these .esps together, since the Creation Kit doesn't seem to heed any sort of load order. Are the changes just merged from the get go (all I did was make some illusion spells refer to new, unique sound descriptors from my own mod) and all I need to do is just save it onto the new patch .esp?

If these are spells unique to SkyRe & Requiem, you will have to load those files as masters in order for the plugin to work correctly. This ensures that they get listed as masters in your new plugin.

The easiest way to do this is to use WryeBash. Boot up WryeBash, and then right click on Skyre_Main.esp and choose "Esmify self"

This sets the esm flag on the file, so that the C.K. will think it is a master file.

Now boot up the C.K., selecting Skyre_main.esp - and don't set anything as the active file.

Once it loads, make your changes and save a new plugin. Your new plugin will have Skyre_main.esp as its master file, and it will now work correctly.

Dont forget to go back to WryeBash and right click the SkyRe file, this time choosing "Espify self" to turn it back into an esp.

Rinse & repeat for Requiem.

I don't think you can fix both in one patch file if that is what you were attempting, I think they will need to be separate patches so that only one or the other is required as a master for users.

I'm only trying to do a patch for SkyRe at the moment. I am only editing the vanilla fury and fear-based spells, assigning new, unique sound descriptors (drawing/sheathing, charging, releasing) to them from my own mod.

So I change the SkyRe-edited vanilla spells to use my sound descriptors, which are listed properly when I have all esps loaded together. And it saves just fine. But when I test it ingame, I get no sounds at all. When I try loading the patch (as the active file, with my mod + SkyRe loaded along with it) I get a warning saying "MASTERFILE: Could not find sound form id (0600489B for magic effect 'InfluenceConfDownFFAimedArea' (0001EA7A), and all the sounds for the edited magif effects have been blanked out.

Does that mean I have to make esms out of both SkyRe and my own mod to create the patch?

Ah, well are your sound files in a .bsa? if they are, you will have to list your mod as a master file so that your plugin can properly access the contents of its .bsa

If they are loose files, you can either set your mod as a master or you can re-make the sound descriptors in your new plugin, referencing the loose files. Probably just setting your mod as a master would be easier and less likely to cause problems.

Also, to follow up - since you say you are only editing pre-existing vanilla magic effects, I don't think you will need to load skyRe as a master like I suggested in the last post - just make sure Skyrim & your mod are masters (use the method above to convert your mod to an ESM temporarily)