Yes, I did this with my Bosch Universal Mixer. I felt that, even at the slowest speed, the mixer rotated too quickly, resulting in dough that was warmer than ideal (e.g., 80 degrees+).
I did/do like the Bosch Mixer, but wanted to slow it down, if possible, without losing what I like about it (which is efficient mixing with the incorporation of air into the dough). The "fix" was to plug the mixer into a lamp dimmer that was then plugged into the wall. It works very well -----it will slow the machine down only so much before it simply stops rotating, and, even if it is still rotating, it is possible to slow it to the point where it really only pushes the dough around, but with a little experimentation, I think it is doing a good job and is an improvement over the lowest factory setting.