^dx12 does not overwrite previous versions.
If you use the update you will have dx9/10/11 & 12 installed on your PC.
Games/software will use whatever DX version driver it is coded for.
You have nothing to worry about- there's no reason not to update it.
Nvidia released a fully dx12 compliant driver set 2 days ago - not sure about amd as I haven't switched my other rig on for a week.