Just documenting this, there are a couple parts to do. Unfortunately I don't have the original sources to credit them but here it is.

To change an NPC's appearance, you have to copy their appearance to yourself (losing your appearance in the process), invoke the Show Looks Menu, then copy it back to them.

# Open console (hit `)
prid player
# In the following capp command, use ID 59a9 for Andreja or 5986 for Sarah.
capp 59a9
# slm player 1 or 2. Use 1 if you want to start from scratch and pick a new Biometric ID.
slm player 2
# Close console (`)
# Drag the body type setting away from the center, then back to the center
# Change the looks however you want
# Hit Save, type name (Andreja), confirm, etc
# Open console (`)
# In the following capp command, use ID 59a9 for Andreja or 5986 for Sarah.
prid 59a9
capp player
# Close console (`)

One idea I haven't tried is first to copy your appearance to a random NPC to store it, then copy it back afterwards (that might work).

To make it persist across Game starts, use this Refresher.txt trick.

Update your Documents\My Games\Starfield\StarfieldCustom.ini file, find the [General] section (creating it if it doesn't exist), and add:

sStartingConsoleCommand=bat Refresher

NOTE: While it seems to be working on 2023-12-26, in the past there has been a problem with Nexusmods rendering the above article text, it's supposed to be "s Starting Console Command" with no spaces between the words. It should look like this screenshot: