Automatically set MTU on netvm change

I have multiple netvms, the MTUs on these need to be set to a specific value to work. Currently I have the following in /rw/config/rc.local :

for I in eth0 eth1
	ip link set mtu 1280 dev $I

This works if the appvm has the netvm set on boot. However if I change the netvm, a new interface is created in the new netvm which has the default MTU which doesn’t work.

How might I have the MTU set correctly automatically?