App/shortcut to quickly change screen lock type?
From what I've read, Tasker should be able to do this.  You can turn on or off the screen lock mechanism based upon whatever criteria you want, including the value of a variable.  You can also change the value of a variable via a widget.  Combine the two and it should work.

Caveat Lector: I've researched Tasker, I've read about what it can and can't do, but I've never tried it (yet).  So take this as speculation.