Have 2 partitions and add HLOD setups to both using HLOD layers that are not shared between them.
Add actors to the second grid and disable "Include Actor in HLOD".
See map check warning:
"Actor /Game/Maps/map_13495398_wp.Cylinder2 has an invalid HLOD layer /Game/Maps/map_13495398_wp_HLOD0_Instancing.map_13495398_wp_HLOD0_Instancing"
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