Create a footer policy in the Global ADOM containing the firewall policies that must be evaluated first, and then assign this footer policy to all other ADOMs.

Create a header policy in the Global ADOM containing the firewall policies that must be evaluated first, and then assign this header policy to all other ADOMs.

Move the FortiGate devices into a single globally scoped ADOM, and merge policy packages, inserting the new firewall policies at the top.

Use a CLI script from the root ADOM on FortiManager to push these new policies to all FortiGate devices, through the FGFM tunnel.