Can't enter tax data to a return that has been submitted. In the past I could for tax planning and 'what if' situations. When will this 'block out' be changed?

Once you have already NETFILED your income tax return, you cannot go back and adjust that return.  However, if you wanted to use a tax return for tax planning purposes, you can create a new return without submitting it.

That was the whole point of being able to make a copy, rename it, and do scenario planning! Creating a new return is just a waste of time. TurboTax needs to fix this.