Row # 632 of CreatureDisplayInfo.dbc corresponds to the Druid Travel Form. I changed the "DisplayID" column (Column 2 for me) from 82 (Tiger.m2) to 453 (StormCrow.m2).
I would rather call it Model ID, to not confuse things while DisplayIDs are stored in CreatureDisplayInfo.dbc.
Yes, this way will definitely work too, you just need to find those displayIDs (which are in DBC I mentioned, at least on WotLK) and just btw, this can change some NPCs, too. It doesn't seem very likely to me that Blizzard would use form's displayIDs for any NPCs but hey, strange things can always happen.
And just btw, you might want to edit also textures used in CreatureDisplayInfo.dbc, not just model. New model can have all textures hardcoded, in that case this will work, but otherwise you would get green texture error ingame until you change texture fields in DisplayIDs data, too.
In the end, my way was quite the same, but much cleaner and safer
. You need to change data used by shapeshifting spell. And its always better to create your own data instead of editing blizzlike ones.