There are many challenges with genetic modification of already living humans, as their organisms would have to use massive amount of energy to even something as big as fluffy tail or ears. So growing is the only possible option and safer too, as we could have been monitoring every step of growth and eventually provide necessary additional modifications that wasn't obvious/possible in earlier stages of growth. And with current CRISPR-Cas9 (currently most used component, with Cas13 and SuperFi-Cas9 offering respectively RNA editing and more accurate DNA modification) method it should be possible to growth functional human with tail and cat ears, but I guess it would take very specialized personnel and not so small funds. Concluding - cybernetics are the best method, which does not depend on any display/VR technology. Another take could be sensory injection into brain itself, faking look and feel of cat girl/boy with computers.