One of the unrecoverable bad moves in PRE is to start a project in the wrong screen ratio. I know there are some hacks to overcome this, but nothing in the main program itself.
I just found out (the hard way ) that DVDAS is more forgiving. I started a project in 4:3 and after about 45 minutes of intense work I realized that it should have been 16:9. But if you right click on the top level and select Properties you can change it! Of course you may have to re-move some of your buttons, etc. but it was a real "WHEW!" for me.