Windows 10 (10.0.14393); how to set registry permissions

I am attempting to fix an "IndirectSound" install so it works with an ancient game called Caesar III. The instructions say I have to modify the registry, so I created a restore point and fired up regedit.

Not surprisingly, I’ve got permissions issues. I fired up regedit as an admin this time – the machine only has one user, I’m using her account, it’s an admin account.

I found the key I was looking for at ComputerHKEY_LOCAL_MACHINESOFTWAREClassesCLSID{1234} but it tells me I don’t have permission to edit a value within that, or to delete a value or create a new one.

I went into permissions for {1234} and set the permissions for the account I’m using to "full control" – same errors. I went back and set the option for "allow inheritance", same errors.

How do I go about changing permissions so that I can edit the keys to try to get IndirectSound working?