Hi,
The imported route is not a BGP route, and therefore the BGP attributes cannot be modified. You can modify BGP routes only when BGP routes are received or advertised.
For example, specifies a route-filter for the routes to be advertised/received to a specified BGP peer.
[~HUAWEI] bgp 262596
[*HUAWEI-bgp] peer xx.xx.xx.xx route-filter Upstream-out export/import