BACK UP YOUR SAVE BEFORE TRYING THIS. This method has anecdotally worked for some, however, you will PROCEED AT YOUR OWN RISK. Save file corruption is a very real possibility, and if you want something for your character that can be accomplished with exec() commands from the console (currently we know the exec commands to give items and skill points for example), use those in-game. This could corrupt your save! So please only do it for your own character features that you can check immediately upon loading into the game.
Using a hex editor such as HxD, load up the sav.dat file and search for (ANSI Text) customization, this string seems to be intact and a good anchor point for finding the character customization data.
Above the customization string, you might be able to see fragments of ANSI text that were not compressed such as nails or jaw. Those variables can be scrambled, but the key here is to find if the ANSI text for two numbers after these strings are intact.
For example, if you can see .aw??07 and you wanted to modify your character's jaw, you are in luck, because that means the number indicating the type of jaw you have is intact, and you can modify that 07 to any of the available options in the character creator (jaw #4 in the character creator, for example, would mean changing the numbers to ANSI text 04). After this modification, swap the old sav.dat for the newly modified one, load into the game, check if your character model has changed and if no weird errors can be seen, congrats, you have changed your character.
Save files use LZ4 compression, and thus direct hex modification is not always possible if the desired variable is compressed as such and not available in plaintext. Save file decompression is possible with CyberCAT by SirBitesALot, but modifying decompressed saves is not possible due to modified, recompressed saves being recognized as corrupt by the system. Currently, it's speculated that there's a variable in the header somehow tied to file size or locations of data, and until we decipher where these checked values are, we cannot fully modify a save.