Dynamic Multi-WAN

I am using mwan3 to load-balance between 2 ISPs.
ISP1 is preferable, ISP2 is inferior.
Due to bandwidth load reasons, I need to keep both in use in load-balance mode[50:50 or 60:40] ratio.
However the load scenario hits only infrequently, like once a week.

So it got me thinking, can the ISP2 brought in dynamically, only in case of load?
I can detect the load by variation in the ping response time.

One simple way would be to detect the load condition, then change mwan3 config and restart mwan3.
That would lead to a bit of disruption.
I am looking more dynmic way.. like add "ip route" or something.

Any thoughts?

A remark here is that load-balancing works on connections and not on individual packets. That means if you load balance 50-50 and one connection to Youtube or Netflix goes to ISP1 and a connection to a simple HTTP page goes to the other, then it is going to be uneven load-wise.
You can fine tune the check_quality options in the interface configuration to have more measurements for the link quality. I think as long as you don't flush the conntrack, the traffic will not be disrupted.