Can you uncouple a tax return after you have completed it to see if this is the beneficial way to file?

You cannot.
If you decide you wish to use individual preparation, you will need to create two new returns.

Thanks

You're welcome!

Do you have to delete the entire return then and create the 2 new ones? And does the deleted return count towards your 20 returns?

If you did not file those returns or print them then they will not count towards your 20 returns. You can delete that return and you will need to complete a new tax return for each person.