Isn’t connmand used by default? So don’t change
/etc/resolv.conf but connmand’ s nameserver config. First list the services:
# connmanctl services *AO SSID wifi_xyz_xyz_managed_psk *A XYZ cellular_IMSI_context123
Next you can change the nameserver:
# connmanctl config wifi_xyz_xyz_managed_psk --nameservers 126.96.36.199
That change should apply to AD as well but will be overwritten by every network change.