An nft style include (implicit or explicit) with position ruleset-pre or ruleset-post should do the trick.
See also Help me update my HFSC shaper scripts for fw4/nftables - #116 by jow
# /usr/share/nftables.d/ruleset-post/01-my-bridge-table.nft
table bridge mangle
flush table bridge mangle
table bridge mangle {
chain prerouting_mangle {
type filter hook prerouting priority -150; policy accept;
iifname "wlan1" meta mark set 0x1
iifname "wlan1-1" meta mark set 0x2
}
}