Azure SQL on VM Availability group Async third node in DR region config

our Availability Groups in Azure are currently 2 nodes, both on the same subnet, with a load balancer in front of them. I'd like to add an async node in another region for DR purposes. This will be on a different subnet. In an ideal world I'd split the current AG nodes onto different subnets, get rid of the LB and update all the connection strings with multisubnetfailover= true. However we have a very old code base and I've been told there isn't budget\time to locate, update and test all the connection strings. If, instead, I updated the cluster with RegisterAllProvidersIP=0, will it work with the LB's and the new DR node? Will failovers between the 2 nodes on the same subnet still have to wait for the DNS TTL to failover?