When bulk enrolling pre-existing devices or auto-pilot devices you can use a custom rule / attribute assignment on e.g. a serial number to move the corresponding devices to a deeper OG which is preferred. Only in a situation with 1200+ devices you might encounter DB maximum issues in SaaS and need to contact support. This was the case for me and my customer and sadly no solution regarding this movement rule, it seems like a hard maximum and conflicts would occur on the database in question.
When using Freestyle Orchestrator with the advanced licens this would not be an issue and you would be able to fix this issue before it can occur, for us the workaround was allowing a top OG enrollment for the devices and manually bulk move to the corresponding OG.
Hope it helps.