As a genjutsu talent with abundant yin, he could just transform the faucet of passive chakra-supply so that when affected by perception- rays or particles the yin blends seamlessly into the surroundings.
Though if the peception is too strong all his passive chakra may be washed up.
If he can make it IMMOLATING CHAKRA that dissolves upon contact with external detection, then putting them in a full genjutsu isn't necessary; solely insofar as they cross or eclipse his existence via scanning jutsu can it affect them.
Different processes in the body are more efficient with requisite chakra natures leveraging their special aspects— replacing everything with yin would mandate multiple times the passive consumption.
However, if he uses half & half —he could arrange the combination in such a way that infringing perception causes an ignition propagating yin chakra exponentially blending perfectly with the environment's chakra signature.
The image received is forced to match an absence of abnormality.
It is like how a placid pond has countless invisible ripples—when a sensor nin sends out a more tangible ripple, those miniscule ripples are collected in a confluence to neutralise the invading momentum so the ripple passes sans disturbance.
This affects the chakra rhythm in the opponent via letting they themselves trip a delusional reading from their own breaking of the balance.
The only thing I can find from the author is the first sentence of a Patreon post on Dec 6th mentioning that he had some health issues. Another Patreon chapter was released yesterday, so hopefully things might be returning to normal and we will hear from him soon.
I literally remember the day I came across your Harry Potter fic. Masterpiece imo, you really inspired me to write and I hope you continue writing because I love reading your work. Thanks a lot.