Got my copy of Mordy's Monsters of the Multiverse. It's got a lot fo slightly revamped creatures. Have you given thought if you will just put a new page number (and possibly update) or do a new line for each? I have to double of a bunch of monsters doesn't sound that appealing.
I am going to just add a page # in MoM at the end of the monsters' entries. If the hitpoints/stats in MoM are roughly the same as the previous values, I will just change them to the new ones. If they are a lot different (like the hit points demon lords from Out of the Abyss and Tome of Foes), I might include them with a slash. Hopefully the stats will be about the same. Generally (but sometimes I forget), I try to include only one entry from a publisher for a monster. For example, there are two entries for giant moray eels (as Dean Martin never sang: when you are swimming in the Mediterranean Sea, and a fish bites your knee, that's a moray), because two different 3rd party publishers had them, and the stats were different even though the CR was the same,
I have started on the races first, and for those (as necessary) I will rename them (and change the stats, size [if necessary] and languages). For ones that used to have subraces like the Aasimar, I plan to hide the subraces. If anyone wants them, they can just unhide rows and get them back, but it will be a little cleaner.
I started a new job recently, and I am really far behind on my D&D reading. I am splitting my attention between the adventure part of Call of the Netherdeep (in case anyone was wondering why none of Alyxian's stats have been added [I am still on chapter 6] and MoM. Once I finish up Netherdeep, MoM should speed up.
Unless there is another UA, the next update will be posted when I finish the races or get one (or more) of the Alyxian entries