It’s a quick transmigration novel, there’s two arcs where the mc is a ger. I think the MC could adjust his body to the peak of perfection?
Ive read so many QT bl they all sorta blend in for me but possible novels Who touched my tail https://www.novelupdates.com/series/who-touched-my-tail/ Quickly wear the Face of the devil https://www.novelupdates.com/series/quickly-wear-the-face-of-the-devil/
Probably Quickly wear the Face Of the Devil. I remember MC could adjust his own settings after he got rid of the control on him. There's one arc where the host is a disguised ger and the ML was an amnesiac general. Another arc is where the host is a ger concubine and the ML was his adopted son.
Could you be looking at arc 5 of Quickly wear the Face Of the Devil? Iirc, the MC goes into the body of a ger who has a weak zhusha zhi, but optimises it to become strong, alongside his body, to the peak of perfection.