Reversing a lens to make it a Macro is a trick that was common when I bought my first Canon SLR way back in the 1960,s. Those 50mm f/1.8 FL / FD lenses can be had for a song (I bought two for $10 each last week at local garage sales), and easily reversed with a inexpensive adapter. I still have some of the macro photos I took back then.
I do admire someone who is able to do good work with one, it does take a lot of care and patience due to the limited focus range.
I have a adapter, and sets of step up / step down rings and have tried it with many old manual lenses. You can freeze the aperture of a EF lens as the user described, but since old MF lenses with adjustable apertures are easily found for cheap, I haven't bothered.