All docs related with installation of all platforms with network costumizations like the example below for bare metal:

https://docs.openshift.com/container-platform/4.15/installing/installing_bare_metal/installing-bare-metal-network-customizations.html#nw-operator-cr-cno-object_installing-bare-metal-network-customizations

In these installation docs we should make a warning about the coded network address for the transit switch subnet the same we have for the join network 100.64.0.0/16

Apart from that with Jiras https://issues.redhat.com//browse/OCPBUGS-36499 and https://issues.redhat.com//browse/OCPBUGS-38440 we introduced a backport in 4.15 and 4.14 on how to setup internal OVN networks, as we have in 4.16+. So on the part for advance network configuration we should specify on how customers can change the masquerade and transit switch CIDRs similar to what we have for the Join  subnet CIDR before installation:

https://docs.openshift.com/container-platform/4.15/installing/installing_bare_metal/installing-bare-metal-network-customizations.html#modifying-nwoperator-config-startup_installing-bare-metal-network-customizations

    OCP 4.14 and 4.15