Change MAC address of VLAN interface
Let's suppose you already have working VLAN setup, and just want to change MAC address of the VLAN interface. In RouterOS v3.24 and 4.0beta3 it's still not possible to change MAC address directly. We'll use bridge for making this possible!
/interface bridge add name=bridge1 disabled=no /interface bridge port add bridge=bridge1 disabled=no interface=vlan1 /interface bridge set bridge1 admin-mac=de:ad:00:be:ef:00 auto-mac=no
Now use bridge1 instead of vlan1 interface (move IP address from vlan1 to bridge1, etc.) - and other devices will see de:ad:00:be:ef:00 MAC-address as a source of packets.