Older FRR versions (<8.4) have a different logic of the as-override option, which confuses and leads to unexpected behavior.
More details:
https://github.com/FRRouting/frr/issues/11677
https://github.com/FRRouting/frr/pull/11692
We should backport changes to 7.5 in VyOS 1.3 to avoid mistakes with configuration and provide the same behavior as in VyOS 1.4.