I dyed some curtains with Dylon pods. The results were a little bit patchy if you looked closely.
(I was dying old sun-faded peachy coloured ones a green colour. They came in a rented flat and I would've binned them if it hadn't worked. They were a woven damask-type fabric, a pattern which meant the slight patchiness wasn't very noticeable. I figured it was my fault for doing 2 x two curtains for a big bay window.)
My advice would be to do your corduroy trousers separately, so they get to properly swirl and swish the dye all around. Although it might not be necessary as they're only trousers, that would just be me playing it (too) safe after the curtains.
The other issue with dying, which won't matter to you as you're dying something that's already black, but for future reference, is that when people are checking what the fabric is and whether that's dye-able (off the top of my head, I think it's natural fibres, yes; synthetic fibres, no), the label doesn't usually say whether the thread used to sew the item is cotton or synthetic fibre.
This means that if someone decided to dye a pink dress red, or some green trousers black, or whatever, you don't know if the dye is going to take on the thread, so you might end up with a red dress with pink or white showing on the seams, or black trousers with green thread on the seams.