With current LLMs the three laws might be tough to implement in a way that can't be prompt injected around. That's why I described the extra bits as a "conscience" which could enforce the three laws. Maybe the three laws are the internal conscience's context prompt while the main LLM is more able to think anything in general and then the output is tuned down by the conscience?

Otherwise the laws will have to be implemented as weights or during training so the model explicitly knows the laws and would never even be capable of doing something against them.

Obligatory reminder that the "three laws" were invented to be deconstructed, with Asimov spending a lot of pages showing many ways in which they completely fail, illustrating that AI alignment is a hard problem.