I have a VLAN subinterface which I need to change the MAC on but I don’t see the option it’s there for physical ether ports
You can’t change vlan interface’s MAC address. What you can do is to create a dedicated bridge, add the said VLAN interface as lone port, set MAC address of bridge interface to wanted value and use bridge interface for communication between ROS CPU and the rest of that VLAN.
with it being a VLAN interface with a VLAN ID set does the bridge need to have VLAN Filtering on or off and if on does the PVID need to match the VLAN ID or just left at 1?
No, the dedicated bridge should be VLAN-ignorant.
Vlan interfaces can be thought of as a pipe with teo ends: the tagged end is attached to it’s “master” interface when vlan interface is created using /interface vlan add name=vlan_interface interface=master-interface vlan-id=VID. The untagged end is “free” and is mostly used as interface (i.e. set IP address on it and let router pass IP packets). And frames either gain or loose 802.1Q header (they get the header when passing from untagged towards tagged end and loose the header when passing in direction from tagged towards untagged end).
But the untagged end can also be used as port of a bridge. As explained previously, frames will be untagged and in your use scenario bridge would be all-untagged (vlan-filtering off).
perfect works a dream, thanks you so much 
When you need to change the VLAN MAC, of course it will change when you change the parent ethernet interface MAC.
Of course the MAC on the untagged VLAN and all other VLANs will change as well, but that likely does not matter.