Its not for me one of my friends install a theme and got screwed out of the treasure hunter trophy.. Now i don't how to break the news. Unfortunately there is no solution. =[
Thank you Aeliana!

PlayStation®3 本体のシステムソフトウェアバージョンが3.10であり、かつ「SPECIAL」よりXMBのテーマをイン ストール後にゲームを終了させなかった場合、ゲームを再起動させるまではトロフィーが取得できない症状を確 認しております。PlayStation®3 本体のシステムソフトウェアを最新バージョンにアップデートしていただくことで問題は解消されます。お手数 をおかけいたしますが、最新バージョンへのアップデートをお願いいたします。

That's what it says on the JP Square Enix website about the theme/trophy glitch, what it boils down to is that the bug affects Firmware 3.10 and below and it has been resolved in newer versions of the Firmware. If you're currently suffering from the problem however, I think you unfortunately need to start over on a new save.

So if you didn't quit after installing the theme then there is no way to unlock the trophies?

The fix is what I mentioned in the guide, "Just to be safe, quit the game after installing these themes..."

Do you remember in Final Fantasy 13 the glitch when you install the theme it would stop you from earning trophies? Did someone discover a fix for that? Thank you. =]

you got the platinum for final fnatsy 13 already. oh my, im so jealous, im so proud that its obtainable.! your the best, hope you write a guide!