1. The taper is there to get the frames spaced at the proper distance (35mm)
2. Yes, you can cut the bottoms off and butt joint them together if you like.
You have a lot of artistic freedom when it comes the frames, they don’t have to look just like a ‘standard’ frame to work. The Mann Lake all plastic frames have a pretty long area for the spacing whereas wood frames are usually less. I prefer less since it gives the bees less area to propolize the frames together.
Another option is to just buy some new end bars from Brushy, I believe you can buy the end bars separately if you like. Sawing small pieces of wood can be dangerous; in some cases it is wiser just to buy new end bars.