How to avoid Assymetric Routing with Fortigate with a new BGP link

To move traffic from the primary link to the secondary link without impacting existing connections when transitioning to a new VRF and interface setup in a FortiGate firewall cluster connected to an ACI fabric, mplement route leaking between VRF1 and VRF2 using BGP to allow communication between the two VRFs without impacting existing connections. This ensures that traffic can flow between the VRFs seamlessly. Create policy routes to redirect specific traffic from the primary link to the secondary link without affecting existing connections. By configuring policy routes, you can control the flow of traffic based on specific criteria, such as source address or protocol.

Until seeing and examining the detailed network diagram including HA compoenents, two VRFs and BGP neighborings, probably nobody would be able to provide any useful information toward the "solutions". Besides, VRF separation and route leaking are two networking mechanisms that could work against each other. There are certain situations leaking specific routes, such as management traffice, while all other other routes/traffic need to be separated/isolated each others.

Also it's not clear if you're concerning about the migration without having a maintenance window or fail-over situations after the migration is done.
But this kind of design consideration is probably beyond this FTNT community.

Toshi