Maybe. There are no guarantees when you're tinkering with these things. It's rare, but I have seen it happen where a program like Partition Magic screwed up during the partition table modification. Fortunately for me it was a brand new system so reloading the OS was only a minor inconvenience. Moral of the story is that things can happen so make sure you've got backups before doing anything. Be prepared for the possibility that things go horribly wrong. Hope for the best, prepare for the worst and all that.
I'm trying to load some older software on a Windows 8 computer with a 2T hard drive that, from research, I've learned requires a C drive that's under 1T. In Windows 8 there's an option to shrink a volume (control panel-admin tools-create/format drive-action-all tasks-shrink volume). If I shrunk the C drive to 800G (it's been defraged and consolidated and only has 300G used) would that work without erasing the operating system? How would I get back the other 1.2T for a secondary drive? The option to create a virtual hard drive seems to want a letter which that section wouldn't have.
I'm hoping to partition the drive without having to reload the operating system.