Place your old HDD into an ext. HDD USB case. That way nothings to be done other than placing in case. You also safeguard it that way. If you require any s/w or such then you have access to it once connected. After awhile, you find you need the space on it, then you can reformat or delete the partition to regain space. You can remove the the old windows section by using s/w that allows such, more easily. Since its on the ext. USB case that alone can be accessed with greater ease. Just be sure your addressing the proper "X" drive.
My ssd is coming tomorrow. Till now i was running on my hdd. I've got lots of files I want to keep from the hdd that wont fit into the ssd. So here is my question can I use my old hdd as a secondary storage without formating it if it has windows on it?