Rancher/Kube - Change default overlay subnet?

We are testing a POC for a Rancher-managed Kubernetes cluster. The default subnet for the overlay network is [] which unfortunately clashes with an existing subnet we have in place.

I really can’t find any good documentation on how you actually change this? Ideally without tearing down everything we’ve built so far, but if this is necessary it can be done.

Single mixed-cluster; 3 Linux nodes (1 worker, 2 etcd/control plane) and 2 Windows nodes (workers). We have issues with the windows nodes connecting to Rancher (the cattle agent keeps crashing, crashbackoffloop) and we believe it could be related to the subnet overlap.

FATA: Cannot connect to https://aa.bb.cc.dd

Running the latest RC release as this has support for Windows ( https://github.com/rancher/rancher/releases/tag/v2.3.0-rc3)

Any insight is greatly appreciated.