"".... is not the same as changing a return that has already been filed."

The software is not the tax return. The software allows you to produce a tax return. Perhaps it would be nice if Intuit automatically produce a copy of the return 'as filed' but they do not.

We fought w/ Intuit for years to get a locking feature and they provided it. Personally, I don't use it.

I change the properties in all my files (generally before each tax season but you can easily do it on an individual basis) to read only.  If there is a software change when you go into the file it you'll see it (and the notification), but can't save it.

edit  As most others, I also save a pdf copy of all returns as filed