if you upgrade, you are using that copy of win7 to justify the upgrade. once that is done, you can no longer use it, even in vm.
If the program you have is not win10 friendly, then it would be best to upgrade. most legit programs have free updates so it will run in win10 but what I have seen so far, if it runs in win7, unless it is an old program, it should run in win10.
I have windows 7 on my main computer, but have had a chance to mess around with windows 10 on my laptop and decided that I liked it enough to upgrade, mostly for the multiple desktops feature. However I have a few programs that won't run on Windows 10. I would be perfectly fine running most of them in a vm, but one of the programs is my antivirus software, which I have a ton of copies of. Is there someway that I could run this in a vm and have it affect the computer, or something else that II could do to use it with windows 10? Thank you!