ebtables-translate -t nat -A POSTROUTING -s 0:0:0:0:0:0 -o someport+ --to-source de:ad:00:be:ee:ff
nft add rule bridge nat POSTROUTING oifname "someport*" ether saddr 00:00:00:00:00:00 ether saddr set de:ad:0:be:ee:ff accept counter

ebtables-translate -t nat -A POSTROUTING -o someport --to-src de:ad:00:be:ee:ff --snat-target CONTINUE
nft add rule bridge nat POSTROUTING oifname "someport" ether saddr set de:ad:0:be:ee:ff continue counter