You can modify the mob's data without commands using this data pack. So you can do it using name tags. Name a mob "Small" to make it small (including armor stands), name a mob "Statue" to make it motionless, name a mob "Silent" to make it silent.
Uninstall: /datapack disable <file name>
Install: Drop zip-file to your server world (in Bukkit-servers, you only need to do this in the main, one world) to the «datapacks» folder.
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