Various heuristics are used during the inventory import process to identify the type of inventory device records. It isn't really something that is intended or open for being changed, and it is only intended that the "virtual machine" type be used for virtualization technologies which FNMS directly supports and can detect itself. You can see some of the heuristics that are used by looking at the WriteVirtualMachines writer procedure in ImportProcedures/Inventory/Writer/VirtualMachine.xml. (This is one of the more intractable procedures, so put on your steel capped boots and hard hat on before entering!)

I would not be nervous about trying to do something outside of the import process to change inventory device types. If you really wanted to give it a shot, I would do a lot of testing to look out for strange and unexpected side effects occurring from such an approach. Consider possibilities like types being flipped back and forth between different values based on which batch process has run most recently, the impact on custom properties (you can have different custom properties for different computer types), and maybe other things.