Migration from SD-WAN BGP on Overlay to BGP on Loopback (FortiOS 7.6.7)

Hi guys,

I’ve been assigned a project where I need to migrate an existing Fortinet SD-WAN environment BGP on overlay to BPG on loopback, and I would like to gather feedback from anyone who has already dealt with a similar scenario because i did not find documentation about this process to be honest.
The current setup consists of a dual-hub architecture where SD-WAN is implemented with BGP running directly over the overlay, using IPsec tunnel interfaces.
All routing decisions are tightly coupled with SD-WAN members, and the entire environment is running FortiOS version 7.6.7 on both hubs and spokes.
The target design is to move away from BGP on overlay and go to BGP on loopabck.
Since I have not found much detailed documentation covering this specific migration path, I am trying to better understand the best approach before proceeding.

In particular, I am interested in knowing whether it is feasible to have a parallel environment, i have 100 sites, so is it possibile to migrate a couple sites to bgp on loopback and still have them able to work with the other non migrated spoke? it is possibile? How the hub can manage this configuration?
 

From an operational perspective, I am interested in any experience related to convergence and stability.
If anyone has hands-on experience with this type of migration, I would really appreciate hearing about lessons learned, design recommendations, or any practical advice that could help make this transition smoother and more predictable.
As said, no documentation is fully covering this topic.

Thank you in advance for your support and insights.