You can absolutely enter CY dates in the PY program. We've done this for 20 years for our planning and accounting clients.

Our folders are FAM20/2020 Clients for all of our 2020 tax year files. When we finish the returns and start on 2021 we simply make a folder called 2021 Clients. We copy the "final 2020" client file over to that 2021 clients folder, roll the year, and use it as the 2021 file.

When the 2021 program comes out we just roll those first, then roll the 2020 folder ones. When we roll we just make sure to only roll the ones from the 2020 folder that have NOT been copied over to the 2021 folder.

Has worked fine for us.