What (AR, FM, TC, DAPAM, etc.) covers “slotting” in the Army?

I would say if there had to be someone in charge, the commander could name one or you could go by date of rank, hopefully everyone is professional enough just to do their job.

Don't remember the reg, but normally the senior (TIG) would be. With that said I as an E6(P) was an acting PSG for 1 yr, cause the BC said so. Also spent time at the PL LDR as an SSG(P)/SFC because the BC said so.

They used to say time in grade accounted for something, but I believe the Cmdr is the one to appoint that leadership position.