I would love to change my MAC Address on Blue interface - Wifi.
I see there is an option in the Web Interface ’ WUI → Network → Assign MAC address ’ but it seems to work only for the RED interface - Ethernet port connected to WAN.
I tried to install ‘MAC changer’ with pakfire but it was “not found”
Correct, this is only for the RED interface.
This option for the RED interface enables you to have the mac address that your ISP is expecting to see.
There is no MAC changer addon package in IPFire.
BTW, why do you need to change the MAC of your blue interface?
Identification in 802.11 is made by SSID. You do not have fixed connection ( by wire ), therfore your client choses the best connection of the known SSID. This enables roaming between multiple APs, all using the same SSID.
Thank you and the reason I was inquiring about changing the Mac
Address. I tried to replace a router that used DD-WRT and somehow it has a feature to change the WIfi Mac as well.
I don’t know why but I was told to use a certain Mac Address.
Maybe it is their superstition 
It works good when using
ip link set eth0 address ... but I don;t know what happens after a reboot