i now have three approx three hundred files listed under my “Scenes” folder in the Binder… is there a way to select them all as a group and change their format to Screenplay?
No, but you can go through a list pretty quickly with the shortcuts Cmd-8 + DownArrow + Cmd-8 + DownArrow over and over.
that worked pretty well - and not too time-consuming… thanks very much for the tip !
You’re welcome. 
For future reference, if the item you have selected is a script item, and you make a new text document, it will be script mode as well. So you shouldn’t ordinarily have to do bulk changes like this (hence the lack of a dedicated feature). This is also true if you Split. So if you’ve imported a long script and want to chop it up, make sure to set that first imported item to script mode, and then do the splitting.
Yeah. I learnt that one the hard way. Not that hitting cmd-8 in each document subsequently is exactly taxing.