SW-Reg voltages at points
maybe not as helpful as the comments (edit: was answers) above, but hopefully more constructive, I've been intending to do this myself recently (and might get round to it tomorrow...).  Injecting a voltage into the junction of the voltage divider (node? ), will add an offset which will change the feedback voltage and hence the output voltage (I think).  Using a digital pot to replace the divider is tricky, certainly the ones I looked at which have 0V as negative supply and generally 5V as positive, with protection diodes on the wiper which won't let you use them with negative rails or positive supplies outside of their own power supply range.  using a DAC to provide  a voltage (via a resistor) to the summing point, should, I hope, allow you to vary the FB voltage and the regulated output.