What needs to happen for this feat to work is for the weapon to add wEasyRace.XXX to itself if the feat is present.
Place the following script on the weapon at Pre-Level, 6000 (the timing is critical, you have a narrow window between when HasFeat.fImpWepFam is set up at PreLevel/5000 and when wEasyRace is checked, at PreLevel/10000).
Code:
if (#hasfeat[fImpWepFam] <> 0) then
perform assign[wEasyRace.Orc]
endif
Note that the Half-Orc race includes support for wEasyRace.Orc, so you don't need to add wEasyRace.HalfOrc, too.
So, for each weapon you want the feat to apply to, replace the existing version with one that includes that script (changing the Race each time, of course).
It also doesn't matter if you check for the hero's race, either. The script that processes wEasyRace.Orc checks that for you, so an Orc Double Axe won't show up as a Martial weapon for a dwarf.
Another note about how this functions; the weapon will NOT show up as proficient in the weapon selector, because the script will not run before the weapon is added to the character. Assigning the tag from the script won't work either, because you can't add a tag to the weapon before it's added to the hero. The weapon will be proficient once added to the character, so you'll want to add a note to the description of the feat that reminds the user of this known bug.