How do I change a unit?

Hello. I'm having a problem when replacing Bone Dragons in the Necropolis. Specifically, the Bone Dragons and Spectral Dragons (Astral Dragons changed as expected). I replaced the Tier 7 Necropolis units with the previous Tier 6 units (i.e., now Messengers instead of Dragons, and I placed another unit in the place of the Messengers). However, after saving the changes and launching the game, their "Skeletons" and "Geometrics" disappeared. And if I understand correctly, the file they referenced was also deleted (Skeletons and Geometrics of the Messengers). No such problems were observed with other modified units! In general, I hope that experts can explain what is wrong. :( ---- *I think this may be related to the fact that the names of the units before the DLCs are very long. They had a problem with embedding. If anything, I'm changing units through the Map Editor (I don't know how correct this method is, but for now, it's the most convenient for me).