If you really want to mod, then get a rheostat or a few, then set it up the way you want. Checking to see what rheostat you need as per amps/voltage.
Maybe even set up a test lab to test it before you install it into the case.
I hate to say the RS words ( radio shack ) but it may be the only place you could find the equipment.
Be rather inventive, expand what you know, built it yourself.
That's what I do in a lot of things, if I can't find what I need, then I build it myself.
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