The immediate issue is you can’t just appoint anyone.
“ Under the Vacancies Act, acting officials generally may come from three categories of government officials: (1) first assistants to the vacant positions; (2) Senate-confirmed officials designated by the President; and (3) certain senior agency officials designated by the President.”
“ Under the Vacancies Act, for instance, certain actions taken by an acting official not serving under its terms “shall have no force or effect” and may be susceptible to legal challenge.”
https://www.acus.gov/recommendation/acting-agency-officials-and-delegations-authority