AFPS 75 has no nomination rule - it has strict criteria about who gets what.
AFPS 05 and AFPS 15 will allow nomination for the receipt of the death in service lump sum or, if the pension is deferred, for the lump sum due if the pension has not yet been put into payment. Like AFPS 75, there are rules about who may receive a dependant's pension but a member can allocate some of his/her pension to someone else. If you put AFPS 05 or AFPS 15 into your browser you will find the scheme booklets which cover this.