I want to make a gradient with less unique colors, so I can do shading for messing about with pixel graphics, but as it is, GIMP's default settings create a very smooth gradient, which ironically is not useful in this case. I want to avoid lowering the color depth of the whole image if I can, however if that is the only way, that could work too. I mostly want a less smooth transition.
To do this you would define your own gradient with several sections, each section being a uniform color. However, if you want more than half a dozen segments this is going to be cumbersome to do wit the gradient editor. But since the gradient file is a just a plain text file, you can make one with a text editor and the help of your calculator or your favorite spreadsheet program (the GGR isn't very far from the CSV). The gradient file format is explained here.