I think that even if you manage to install the old PSP9 on your W10, at any point, a future update can break it again.
As for the color correction command, are you talking about the Manual Color Correction that was under Adjust > Color Balance? If so, it is not gone; it is just hidden. You can retrieve it by going to View > Customize and on the Commands tab, click on the Unused Commands and then scroll down on the right pane until you find it. Click on it, and drag it where you want it, and you will have that command back at your fingertips.
That is how you can retrieve any command that seems to have gone missing over some versions.