Becoming a genius loci
A genius loci differs from a loci spirit primarily through its focus on a specific powerful mortal soul, and a mortal might be able to become a genius loci through ritual magic, though the process depends on the individual much like the process of becoming a lich.2
Infusing a place as a genius loci imbues it with traits of the source soul, including its alignment and personality, that alter the area's natural laws in ways similar to planar traits. The affected area of a genius loci infusion can span from one to many miles in radius, and people within that area receive visions and portents before the process is complete.2
Once infused, a genius loci is difficult to remove. Any of its worshipers must either renounce their beliefs or be destroyed, its manifestations must be removed, and the core soul must be made manifest and then destroyed.2
- Genius loci on Wikipedia.