the recommended way to replace a disk is to run vxdiskadm and go for option .
there are normally two scenarios needing to repalce a disk - disk failed or remove a disk then replace it with a new one. For either operation please consult with the technotes below.
To replace a failed disk https://www.veritas.com/support/en_US/article.000035402
To remove and repalce a disk: http://sort.symantec.com/public/documents/sf/5.0/hpux/html/vxvm_admin/ag_ch_disks_vm36.html
Running other vx* commends (like vxplex, vxsd, vxmake, vxdisk, vxassist etc) to replace a disk is not recommended