By looking at the rest of the 317 protocol, there doesn't seem to be a way to change the list dynamically. It seems as though that whenever the player decides to add or remove a player from their list, it must send all the values again.
=== Packet Structure ===
{|border=2
! Data Type
! Description
|-
| [[Data Types#Standard Data Types|Long]]
| The Unique Identifier of the player(s) (possibly determined by their username).