I'm pretty sure I've figured out how to merge them reliably. So first and foremost you'll need Yabber (link in main description).

Once you have that set up you'll want to use it to unpack your current c0000_a9x.anibnd.dcx, then go to ***\c0000_a9x-anibnd-dcx\GR\data\INTERROOT_win64\chr\c0000\hkx\a9x_compendium and paste the HKX files from this mod.

If you were doing TAEs this would be the end of the process but this requires one extra important step:
Navigate back to the c0000_a9x-anibnd-dcx folder (the one with "GR") and open the file titled "_yabber-bnd4.xml" (download notepad++ if you can't open it) you'll then want to go all the way to the bottom and include these lines before the </files> line:

    <file>
      <flags>0x40</flags>
      <id>1944000003</id>
      <root>N:\</root>
      <path>GR\data\INTERROOT_win64\chr\c0000\hkx\a9x_compendium\a944_000003.hkx</path>
    </file>
    <file>
      <flags>0x40</flags>
      <id>1988030020</id>
      <root>N:\</root>
      <path>GR\data\INTERROOT_win64\chr\c0000\hkx\a9x_compendium\a988_030020.hkx</path>
    </file>

Here's an example of what the end of the file should look like afterwards