A virtual Ethernet adapter has the following attributes:

$ lpar help cheth
USAGE:
   lpar [-h <hmc>] [-m <ms>] [-p <profile>] cheth [-d] [-f] [-i] [-I] [-l <detail_level>] [-q <qos_priority>] [-r] [-R] [-s <vswitch>] [-t <trunk_priority>] [-w <wait_time>] [-v] <lpar> <slot> [<attributes> ...]

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Valid attributes for DLPAR and profile:
   ieee_virtual_eth - IEEE 802.1Q compatible
      0 : no
      1 : yes
   addl_vlan_ids - comma separated list of additional VLANs
   qos_priority - QoS priority
      none : no QoS
      0-7 : priority to use
 
Valid attributes for profile only:
   port_vlan_id - VLAN-ID for untagged packets
   is_trunk - trunking port (VIOS only)
      0 : no
      1 : yes
   trunk_priority - priority of the trunk adapter
      integer betwen 1-15
   vswitch - virtual switch to connect adapter to
   mac_addr - MAC address to use
   allowed_os_mac_addrs - allowed MAC addresses
      none : OS defined MAC addresses are not allowed
      <mac>[,...] : comma separated list of 1-4 MAC addresses
      all : OS defined MAC addresses are allowed

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$

Some attributes like ieee_virtual_eth, addl_vlan_ids and qos_priority can be changed online. All other attributes can only be changed in the profile of an LPAR, e.g. port_vlan_id or vswitch.
The command to change virtual Ethernet attributes is “lpar cheth“.