If you have your Windows 7 disc and product key you can always do a clean install by booting to the Windows 7 disc, formatting your Windows 10 drive, installing Windows 7 again, and starting over. The operative phrase is starting over. If you choose to do that you will lose all of your programs and your data. If you choose to do that, make a backup before you install Windows 7.
Your Windows 7 system files are stored in C:\Windows.old. According to the article here, after 30 days Windows 10 automatically deletes the C:\Windows.old folder. If yours is deleted, then you will need to backup your files and do a fresh install of Windows 7 on your computer.
Your other option is install Windows 7 as a virtual machine in Windows 10 and run your programs that don't work in Windows 10 in the virtual machine.
I hope that helps answer your questions.