Basically yes. The hardest probably is to do this retroactively, right from the beginning it's much easier.To your second point, you mean as in the ability to personalize and/or segment the nickname system based on their current environments? I.e., if Shani and the MC are exploring a Zone or out on Stalker-related work, they would have a more professional naming convention/nickname in place whereas if they are at home and/or doing non-related Stalker work, then their nicknames would be more affectionate and/or amicable in nature.. to reflect their immediate environments and/or current task at hand
If so, that would be interesting to see, but maybe more difficult to code in I presume because the game would have to factor in the environment they are in and know when to set the proper nicknaming alias based on the defined scripted event in question....
Like, there is already a Nickname System in place and so are the variables/flags to input the chosen Nickname. The difficult thing is probably to make it differentiate between Shani and Ain, and any other future Character using a (customizable) Nickname for MC. It's doable I think, but with the length of the AVN it's a ton of (extra) Work. Especially if you want to expand the System to also make a difference in what Situation the Interaction is happening.
Would it be not customizable it would be much easier as it would be just a writing thing. Like for Ain it's just always "Daddy", for Shani in the beginning "Dad" or "Father" when she's with him in Official Business affairs. Later on "Daddy" like Ain does but only in intimate/Sexual Situations like at Home after her Initiation or when they are with the Princess in the Bath etc.