Yeah. Supreme court ruled that political parties post-2016 are private clubs that can do whatever the fuck they want (Supreme Courts ruling on DNC's ratfucking of Bernie).
Afaict from DNC rules , Biden needs to release his delegates for the first rounds of voting; from there it would proceed like any convention prior to 1976.
Honestly, it would be a great thing for the Democrats to do this. All of a sudden people would really fucking care about the election.