Assuming that un.txt file contains the device IDs ("naa.xxxxxx"), you can do
$esxcli.storage.core.device.set($_,$null,$false,'on')
where $_ is the device ID, the 2nd parameter is a new name for the device if required (otherwise specify $null).
The 3rd parameter is a Boolean indicating if the device should be non-=persistent or not.
The last parameter defines the state can have 'on' or 'off'.