Guess I will have to come up with a more unique name for my mod. :P I feel that craftable synths & synth parts should probably be done at a different workbench apart from the robot workbench. Synths & robots don't seem compatible, & voice clips from the robots seem to confirm this. Making the synths piecemeal akin to the robots doesn't seem possible unless you completely change the synth class, Bethesda built them as two pieces same as the rest of the npcs, humans, ghouls, super mutants etc. However, what may be more plausible is having the synth mods not be visible, just add effects. This could possibly be done through adding perks. The only way I see settlers being modifiable is either through perks ("cybernetic implants") or by converting them to robobrains. Same goes for the creatures. Just my two cents. Good luck to you!