Switching the master role, was only introduced in  version 5.1SP1.

Here is an extract from the release notes.
Veritas Storage Foundation™ for Oracle® RAC Release Notes 5.1 Service Pack 1

Changing the CVM master online
Cluster Volume Manager (CVM) now supports changing the CVM master from
one node in the cluster to another node, while the cluster is online. CVM migrates
the master node, and reconfigures the cluster.

Veritas recommends that you switch the master when the cluster is not handling
VxVMconfiguration changes or cluster reconfiguration operations. In most cases,
CVM aborts the operation to change the master, if CVM detects that any
configuration changes are occurring in the VxVM or the cluster. After the master
change operation starts reconfiguring the cluster, other commands that require
configuration changes will fail.

To change the master online, the cluster must be cluster protocol version 100 or
greater.

Here is a testing I carried out for version 5.1SP1 and it works fine.

1)Version is Solaris 10, running VRTS version 5.1SP1

Node-03# uname -a
SunOS Node-03 5.10 Generic_141444-09 sun4u sparc sun4u
Node-03# pkginfo -l VRTSdbac
   PKGINST:  VRTSdbac
      NAME:  Veritas Oracle Real Application Cluster Support Package by Veritas
  CATEGORY:  system
      ARCH:  sparc
   VERSION:  5.1
   BASEDIR:  /
    VENDOR:  Veritas Corporation
      DESC:  Veritas Oracle Real Application Cluster Support Package by Veritas
    PSTAMP:  5.1.100.000-5.1SP1-2010-10-01_10.10.00  
  INSTDATE:  Apr 08 2011 00:09
    STATUS:  completely installed
     FILES:      217 installed pathnames
                  33 shared pathnames
                   5 linked files
                  56 directories
                 133 executables
               10140 blocks used (approx)

2) Confirm the master node is on Node-03 with these commands:-

# vxdctl -c mode
mode: enabled: cluster active - MASTER
master: Node-03

Node-03# vxclustadm nidmap
Name                             CVM Nid    CM Nid     State
Node-03                      0          0          Joined: Master
Node-04                     1          1          Joined: Slave
Node-03# vxclustadm -v nodestate
state: cluster member
        nodeId=0
        masterId=0
        neighborId=1
        members[0]=0x3
        joiners[0]=0x0
        leavers[0]=0x0
        members[1]=0x0
        joiners[1]=0x0
        leavers[1]=0x0
        reconfig_seqnum=0x9dfc12
        vxfen=off

3) Now switch the master node to Node-04:-

Node-03# vxclustadm setmaster Node-04

4) To monitor the master switching
Node-03# vxclustadm -v nodestate
state: cluster member
        nodeId=0
        masterId=1
        neighborId=1
        members[0]=0x3
        joiners[0]=0x0
        leavers[0]=0x0
        members[1]=0x0
        joiners[1]=0x0
        leavers[1]=0x0
        reconfig_seqnum=0x9dfc12
        vxfen=off
state: master switching in progress
reconfig: vxconfigd in join

Extracted from the messages file during the switch
Jul 13 17:44:02 Node-03 vxvm:vxconfigd: [ID 702911 daemon.notice] V-5-1-1590
6 CVM_VOLD_MS received
Jul 13 17:44:02 Node-03 vxio: [ID 327305 kern.notice] NOTICE: VxVM vxio V-5-
3-1569 vol_check_try_msw: sending MSW-IOQ-START bcast
Jul 13 17:44:02 Node-03 vxio: [ID 699473 kern.notice] NOTICE: VxVM vxio V-5-
3-1571 vol_check_try_msw:MSW-START GABbcast sent
Jul 13 17:44:02 Node-03 vxio: [ID 638311 kern.warning] Warning: VxVM vxio V-
5-3-1503 cvm_msg_get_nid_master: dropping nid message for master switching.
Jul 13 17:44:16 Node-03 vxio: [ID 136199 kern.notice] NOTICE: VxVM vxio V-5-
3-1581 Master switch is complete

5) Then verify the switch has been successfull to node Node-04.

Node-03# vxclustadm nidmap
Name                             CVM Nid    CM Nid     State
Node-03                      0          0          Joined: Slave
Node-04                     1          1          Joined: Master

Node-03# vxdctl -c mode
mode: enabled: cluster active - SLAVE
master: Node-04