H2O, you're dealing with two systems that are mutually exclusive in a fundamental way. Schoeps' system is based on active accessories (the FET circuitry is in the cable, gooseneck or extension tube) while Neumann's system is based on active capsules (the FET circuitry is built into the short, barrel-shaped adapter that's attached to the back of every capsule). Either way you run it, you've either got one FET stage too few or one too many--in addition to pins, threads and shells that are all incompatible.
Jörg Wuttke invented active accessories for condenser microphones while he was chief engineer at Schoeps, and he patented them along with Dr. Schoeps in November, 1973. The "Colette" system became quite successful throughout the world, and soon Neumann and other manufacturers wanted to introduce their own quasi-equivalents. But being honorable people, and (I would infer) having enough self-esteem as engineers that they didn't want to just imitate someone else's solution, Neumann went a different way in their KM 100 system, which was introduced in 1988.
The amplifier circuitry of both manufacturers is sonically transparent, however. There's no frequency contouring or "euphonic distortion" or other sound shaping in the circuitry; it's just an impedance converter (a current amplifier, basically). Thus there would be little to no chance of hearing any difference between them except under contrived circumstances--there might be a dB or two of difference at 20 or 25 Hz, for example. For normal recording applications I wouldn't expect there to be any humanly perceivable sonic difference at all.
But I do sympathize with the urge to do it anyway, just to hear it for yourself. I'll admit that I wanted for some time to graft the original KM 84 capsule head and reflector onto KM 100-series (or KM 180-series) amplifier bodies. It's all the more frustrating because Neumann actually made a batch of microphones that way at one point for a customer in Japan (the so-called "KM 184 A")--but they don't make or sell that version of the microphone any more.
--best regards