pfSense

192.168.88.44 - CARP VIP (VHID: 1)
192.168.88.45 - IP Alias on CARP VIP:

[2.6.0-DEVELOPMENT][root@pf100.home.arpa]/root: ifconfig vtnet0
vtnet0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0 mtu 1500
    description: LAN
    options=800b8<VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,LINKSTATE>
    ether ce:44:5c:c1:e6:8c
    inet6 fe80::cc44:5cff:fec1:e68c%vtnet0 prefixlen 64 scopeid 0x1
    inet6 fc00:88::100 prefixlen 64
    inet 192.168.88.100 netmask 0xffffff00 broadcast 192.168.88.255
    inet 192.168.88.45 netmask 0xffffffff broadcast 192.168.88.45 vhid 1
    inet 192.168.88.44 netmask 0xffffff00 broadcast 192.168.88.255 vhid 1
    carp: MASTER vhid 1 advbase 1 advskew 0
    media: Ethernet 10Gbase-T <full-duplex>
    status: active
    nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>

After changing CARP VIP VHID to 2, the IP alias remains on the old VHID 1:

[2.6.0-DEVELOPMENT][root@pf100.home.arpa]/root: ifconfig vtnet0
vtnet0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0 mtu 1500
    description: LAN
    options=800b8<VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,LINKSTATE>
    ether ce:44:5c:c1:e6:8c
    inet6 fe80::cc44:5cff:fec1:e68c%vtnet0 prefixlen 64 scopeid 0x1
    inet6 fc00:88::100 prefixlen 64
    inet 192.168.88.100 netmask 0xffffff00 broadcast 192.168.88.255
    inet 192.168.88.45 netmask 0xffffffff broadcast 192.168.88.45 vhid 1
    inet 192.168.88.44 netmask 0xffffff00 broadcast 192.168.88.255 vhid 2
    carp: MASTER vhid 1 advbase 1 advskew 0
    carp: MASTER vhid 2 advbase 1 advskew 0
    media: Ethernet 10Gbase-T <full-duplex>
    status: active
    nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>