To make a Pokémon appear like it was obtained in a trade it needs to have the "Link Trade" encounter location, rather than Route 10, or whatever. If a Pokémon is traded it loses its physical encounter location and gains the Link Trade location. Also, for ALL Gen 5 Pokémon, the "Encounter" drop down list is ALWAYS set to Egg/Pal Park/Event/Honey Tree/Shaymin. Don't ask why, it just seems to be the way the game works.
If you want it to have your OT, you still can, because eggs can be traded too. So give it your OT, set its encounter location to Link Trade, its Encounter status to Egg/Pal Park/Event/Honey Tree/Shaymin and check the "As Egg" box, and then choose any Route from Pokémon Black as its hatch location. You shouldn't have to do anything else - the date doesn't have to be changed because it should automatically change itself to today's date, which is totally plausible.
Another thing to note is that if you're giving a Pokémon its Dream World ability, then you need to add 1 extra byte to the (0x42) option under the OT/Misc tab.
Rather than using legal.exe, I would recommend temporarily making Braviary level 50 (if it isn't above level 50 already) and putting it along with at least 2 other Pokémon in your party (all of which must be over level 50, non-legends and obtained legitimately, just to be safe) and try to go into the Random Matchup server. If a Pokémon is viewed as illegal by that system, it will say "There was a problem with your Pokémon and they could not participate", and kick you out of the server. Nothing will happen to your Pokémon but this is an easy way to check if the game considers it legal or not.
Hope this helps and don't hesitate to PM me if you continue to have problems.