Adjustable DC/DC converter and/or LDOs for space application
How about an interesting idea. Not sure if it's perfect solution or even correct one, I hope someone adds to my comment confirming/busting it. But it won't hurt if you just try it on a breadboard.
Your LDO must have an external voltage divider to set its output voltage. How about you replace one of them with digital potentiometer? The one that works with I2C. You can change one resistor, thus you can change output voltage with reasonable steps via I2C. Of course, you have to see for yourself what exactly its resistance swing should be. You can even have two of them for finer tuning (then you probably need two different ones so that their slave addresses don't match or they should have I2C address select pin; or address shifter, which is too much extra circuit imo).
A little unorthodox solution, but I would try it on breadboard just for fun first, there's a good chance it will work. Especially with two digital pots. But be careful when changing voltage with 2 variable resistors, they will change values not at the same time, which may lead to problems.