Can you still do the whole fletch while you fish thing? I was thinking of doing broad bolts while barb fishing just to put a dent in my fletching.

You can low alch

 

I dont think you can do any fletching seeing as the whole interface comes up and then you gotta click the icon in the middle and its bound to take at least a tick

can, but it's much more difficult and less fruitful(as far as fletching is concerned) nowadays. If you want to multytask fishing, try low+high alch barb fishing.

I seen bu11seye00 do something like that for woodcutting. Once you get a fish, use heads -> unf bolt and quickly click the make all interface and reclick fishing spot.

They've since made bolts "make-x" which makes it very difficult to do that, though it was possible until quite recently.