If you can program in Flash, you might want to create a Flash screen, which lets you do just about anything you want.
Doing that with a standard screen would be much harder, if it's possible at all. The only way to enter text, that I know of, is with a TextBox, or InputBox. Neither of which would normally be displayed on the screen, as they are only displayed while the macro is running.
I think you'd need to close the file, then change it, then reload it. That shouldn't be too hard to do, but getting it as seamless as you'd probably like may not be possible.