how to change mount point parameter of backup-volfile-servers or --volfile-server online for Single point of failure?

[adu99999]

Description of problem

we have multi cluster of glusterfs, such as node1 node2 in cluster A,
node3 in cluster B, cluster B has a volume named data (replica 2);

1 node1 will mount glusterfs volume data, such as: mount.glusterfs node3:data /data
2 then we add node4, migrate data brick to node4; and expand volume to node5 node6 node7;
3 if node3 is down, node1 can not connect to 24007 in node3, can not know the changes in this data volume; so we need add node4 to mount process of glusterfs; if node3 24007 down, then node4 24007 will up, keep running;

we do not want to umount volume for so many node mounted;

Question
is gluster can change volfile-server online , and how to solve this problem， thanks.