The format of these for every race, vanilla or otherwise, is the same. But this is a tutorial for how to patch my two race mods, as in, I'll provide you specifically with information to patch for demon or solar. 

You've got to dig for the race id of other races yourself. 

I'll also write assuming you know nothing at all about fiddling with mods.

• BG3 Modder's Multitool: https://github.com/ShinyHobo/BG3-Modders-Multitool
• Notepad++: https://notepad-plus-plus.org/
  

• Run the installer for Notepad++.
• Unzip the BG3 Modder's Multitool and put it somewhere outside Program Files. (Legit installation instructions here: https://github.com/ShinyHobo/BG3-Modders-Multitool/wiki/Installation)
• Open up the application named "bg3-modders-multitool" and atop the window, go into configurations. (Legit configuration instructions here: https://github.com/ShinyHobo/BG3-Modders-Multitool/wiki/Configuration)
• Or just direct to it your bg3.exe location, (e.g. C:\Steam\steamapps\common\Baldurs Gate 3\bin\bg3.exe).
• Then direct it to your game Document's location, (e.g. C:\Users\Bob'sYourUncle\AppData\Local\Larian Studios\Baldur's Gate 3)
• Check the box that says "Pack .paks to Mods folder instead of zipping." *When in doubt, don't tick this box. Mod manager will give you a zip file instead, exactly like the one you would download from me, then you can do with it what you like.
  
  

• Play the CC mod. Know what you want. Jot their display names down. I'll use my Not Aylin head as an example. The head's just called Not Aylin, go figure.
• Drag the cosmetic mod into the blue box in the multitool so it unpacks. Then, on multitool's top bar, select Shortcuts\UnpackedMods so it takes you to the loose files.
• Go to UnpackedMods\LAR_NotAylin\Localization\English\LAR_NotAylin.loca.xml, or any document that ends with .xml. Open it up with Notepad++ and command-f for the display name, record the long string of number associated with it, e.g. Not Aylin is h205e885bg04a5g4725g814cg158ff51470ed.
• Now, go to UnpackedMods\LAR_NotAylin\Public\LAR_NotAylin\CharacterCreation\CharacterCreationAppearanceVisuals.lsx, and command-f for the same string of number. There will be a bunch of entries with it, but you only need one/some of them.
  
  For demon, I'd recommend sticking to whatever was made for drow: aka, entries with a race id of this:
  <attribute id="RaceUUID" type="guid" value="4f5d1434-5175-4fa9-b7dc-ab24fba37929"/>

  For solar, I'd recommend sticking to whatever was made for half elf: aka, entries with a race id of this:
  <attribute id="RaceUUID" type="guid" value="45f4ac10-3c89-4fb2-b37d-f973bb9110c0"/>
*One of them starts with 4f5, one of them starts with 45f. They're kind of close, so take care if you're eye-balling it.
  
  If you insist on round ears, human stuff have an id of this:
  <attribute id="RaceUUID" type="guid" value="0eb594cb-8820-4be6-a58d-8be7a1a98fba"/>

• You can narrow it down more by looking at body shape( 0 slight, 1 built), and body type(0 male, 1 female).
• Copy the relevant nodes (from <node> to </node>) into your DIY CharacterCreationAppearanceVisuals.lsx at DIYRaceCCPatch\Public\DIYRaceCCPatch\CharacterCreation
  

• Depending on if your're patching for solar or demon, the RaceUUID have to be changed accordingly. E.g.
  

Demon: af52d07e-5561-4bd7-9614-28ffe15925a7
Solar: 380159a0-602e-4d89-bc61-11fd7174c5b8

• Just copy those in place of the original drow/human/half elf IDs
• Then, pull up multitool again. Click the Generate button under v4 UUID/TranslatedString Handle Generator, make sure the "Handle" box is not ticked, then click on the string of numbers and letters once to copy it
• On every node, where it says "id="UUID" type="guid"", paste your new string in place of the old one
• Do this for every node. They each have to be unique.
  

• Navigate back out to the outermost DIYRaceCCPatch, and drag the entire folder into the blue box in Modder's Multitool. There will be messages telling you it worked (e.g. [11/17/2023 16:37:39] DIYRaceCCPatch pak moved to Mods folder!).
• That's it!
  

• Follow various set up steps listed above, if haven't done so already.
• Unpack the cosmetic mod you wish to be made compatible with modder's multitool. On the multitool's top bar, select Shortcuts\UnpackedMods.
• Navigate to UnpackedMods\[Target-mod-name]\Public\[Target-mod-name]\CharacterCreation\CharacterCreationAppearanceVisuals.lsx. Search for one of these UUIDs below:
  
  Human: 0eb594cb-8820-4be6-a58d-8be7a1a98fba
Githyanki: bdf9b779-002c-4077-b377-8ea7c1faa795
Tiefling: b6dccbed-30f3-424b-a181-c4540cf38197
Elf: 6c038dcb-7eb5-431d-84f8-cecfaf1c0c5a
Half-Elf/Half-Drow: 45f4ac10-3c89-4fb2-b37d-f973bb9110c0
Dwarf: 0ab2874d-cfdc-405e-8a97-d37bfbb23c52
Halfling: 78cd3bcc-1c43-4a2a-aa80-c34322c16a04
Gnome: f1b3f884-4029-4f0f-b158-1f9fe0ae5a0d
Drow: 4f5d1434-5175-4fa9-b7dc-ab24fba37929
Dragonborn: 9c61a74a-20df-4119-89c5-d996956b6c66
Half-Orc: 5c39a726-71c8-4748-ba8d-f768b3c11a91
Or additional non-vanilla races, if they are in the document and you know their ID

• Select a race similar to your new one (Tip: most human-like tall races have identical hairs), pick the race you play with the least. Note that the chosen race will no longer have access to its character creation items.
• Find and replace all of the chosen race's UUIDs with a new race's. E.g.
  
  Demon: af52d07e-5561-4bd7-9614-28ffe15925a7
Solar: 380159a0-602e-4d89-bc61-11fd7174c5b8

• Save your changes.
  

• Navigate back out to the outermost folder of the cosmetic mod, drag the entire folder into the blue box in Modder's Multitool. There will be messages telling you it worked (e.g. [11/17/2023 16:37:39] XXX pak moved to Mods folder!).
• Use this edited cosmetic mod in place of the original. To reset, you can redownload a copy of the original or manually reverse your changes.