They didn't "change" it. They fixed it. The original appearance did not look like advertised on the pack, so people were complaining about that. Now they fixed it so that it would match the ad on the pack.
And where in the advertisement was it said that those specific pieces shown were the Phantom and Spymaster pieces? Exactly nowhere. Handdrawn advertisements are just interpretations of how the items look. They are NEVER reliable examples of the actual item. Never meant to be either, otherwise EACH cartel pack should contain a full Revan set and every other piece of clothing displayed as well, all pets shown, and maybe even give you a companion looking like every character displayed on the package.
The preview button exists specifically to show how the items look in game, and even on your own character or companion. Both were rather uncommon drops from Cartel Packs, both were Bind on Equip.
Don't like their appearance? Simple: put them on GTN and sell them for several hundred thousand.
Do like their appearance? Simple: look through the GTN, make sure to preview, and buy them if you like them.
However, the items were changed DRASTICALLY in appearance AFTER purchases have been made, items have been equiped and thus, items have become bound to character. This change needs to be reverted, and FAST. Especially on the Phantom and Spymaster sets, since those two sets were altered radically, while the other sets were also altered, but more subtle.
I can already see the value of the chestguard dropping from it's current 400-500k to less than 30k. Traders are very reluctant to relist the ones they have in storage, a lot of them have probably been flipping the thing like crazy over the past month, and now see their investment turn into a profit loss, hoping for a revert or waiting to see where the new value settles. I'm glad I'm not one of them, since I don't like flipping, but I personally wouldn't even give 5k for it as it looks now, whereas the old design had me look a few times whether I should save up for it on some toons.