Physically migrating Internet BGP router for a client

Hi folks,

As stated in the title, I'm in the process of migrating an Internet BGP router for a client, going from a ISR3945 to a ISR4461. This router connects to one ISP, and another interface connect to internal segment (iBGP router, as well as downstream firewall pair which runs static routes)

Customer's current router does not have any optimisation to timer, so 60/180 without BFD. It does have a backup router which connect to another ISP.

Me and my colleagues try setting up a lab to see which migration method would incur the least downtime without changing current configuration (since 24/7 service). We found out by QUICKLY migrating the physical links to the correct ports on the new router, the BGP session on the simulated ISP router would not be teared down, and only 3-4 packets dropped (9-12s). The new router would establish the BGP session and learned new routes.

Since the config is not changed, the rollback process would occur just in reverse order.

Is this a valid migration method in real world, considering the router is learning like 10K-ish routes from the directly connected ISP alone (default + ISP customer routes)? Of course this would happen during scheduled MW, but we would like to minimise downtime as much as possible.