Run nisprefadm with the -m server=server(new) option.
#nisprefadm -L|-G -C name -m oldserver=newserver(n)
-L|-G determines whether you are modifying a local file or a global table.
-C name is the IP number of a subnet or the name of a machine. This option is only used when you are also using the -G option. The modifications you make with this command apply to the subnet or machine that you name.
-m is the modify server list option.
old server is the name of the server whose preference number you want to change.
new server(n) is the server name and its new preference number.
For example, on the deneb machine, to change the number given to the replica6.manf server to 2 in deneb's local client_info file:
deneb# nisprefadm -L -m replica6.manf=replica6.manf(2)