change and push a new hostname to the mongodb cluster.

gistfile1.sh

cluster1:PRIMARY> conf = rs.conf()
{
        "_id" : "cluster1",
        "version" : 98579,
        "members" : [
                {
                        "_id" : 0,
                        "host" : "shortname001:27017"
                },
                {
                        "_id" : 1,
                        "host" : "long.name002.com:27017",
                        "arbiterOnly" : true
                },
                {
                        "_id" : 2,
                        "host" : "long.name003.com:27017"
                }
        ]
}
cluster1:PRIMARY> conf.members[0].name = "long.name001.com:27017"
cluster1:PRIMARY> rs.reconfig(conf, { force: true } )