A legal and regulatory question about First Doses First

It isn’t clear to me who in the United States is legally entitled to make this decision.  An FDA EUA is required before a vaccine can be used in the U.S.  But once an EUA has been issued, is “off-label use” permitted?  The CDC’s Advisory Committee on Immunization Practices recommends how scarce vaccine doses should be prioritized, but “states” (governors?) are free to make contrary prioritization decisions.  Can states also decide to give half-doses or lengthen the interval between first and second doses?  Can a hospital, a nursing home, or an individual doctor make such a decision?  (If so, can it also deviate from its state prioritizations?)  Can HHS or the President specify how these decisions must be made, or alternatively can they explicitly free lower-level decision-makers to use their own judgment?

You’re not a specialist in pharmaceutical law, I realize.  But I doubt you’ll let that stop you!  When you recommend a less risk-averse approach to COVID-19 vaccination, to whom are you addressing the recommendation?  Who has a right to implement it?

That is from MR reader Peter Sandman.  Can any MR reader inform us on this?