Self Nepotism

Self nepotism would be giving yourself a new role because of your power. Declaring myself the king of my bedroom would be self nepotism.
A specific kind of "Narcissism with power"

credits to redcactus23_5211 for proper definition

'I hate my boss so much, he just appointed himself in charge of the department of Cheese making. We're a law firm. This is self nepotism to such an extreme degree'