I just loaded a Birth By Sleep Final Mix PSP save on my PS3 and it works fine! Just follow these steps:
1. Use SaveGame Deemer or SED or JPCSP or any other PSP savegame decrypter to decrypt a PlayStation Portable BBSFM save. For SGD, the decrypted files will be in the SAVEPLAIN folder.
2. Copy a Birth By Sleep HD savefile to a USB
3. Use Bruteforce Save Data 4.7.4 to load your save and Decrypt PFD(All Files) [You will have to open your PARAM.SFO to get your UserID and ConsoleID]
4. (Optional) Edit the PARAM.SFO to match your new stats
5. (Optional) Use Kingdom Hearts BBS - Save Editor v0.4 to edit D-Links you couldn't normally obtain into your character
6. Update PFD(Partial)(All Files)
7. Encrypt PFD(All Files)
8. Verify PFD
9. Override your old save with the new one
This was possible due to the fact that no actual new game content was added between the Re/Final Mix and HD versions of the games; in fact, the SD Jap versions' serial numbers can even be found in the save folders names! Because of this, I believe that with a variation of this method using a PS2 save decrypter, you could very well import old saves from every PlayStation Kingdom Hearts game to the HD versions. I'm fairly confident of this, because this is not the first time I've region-transferred a Square Enix game; Deus Ex The Fall iOS saves and PC saves are also interchangeable.
This process causes a few minor glitches, though, as I will denote below.
If you use save editor to enable Vanitas D-Link, you can't disable it in the menu, possibly because it has no name in the regular files. However, I enabled it on a Ventus save where I also had a Multiplayer D-Link, and while the multiplayer D-Link was not available, its custom name could be selected in the D-Link menu to activate the Vanitas D-Link.
Changes made to Birth by Sleep HD from Final Mix:
Several one button-pressing Shotlocks became random sequences of the four different buttons.
The buttons are shown in their respective PS3 colors if displayed
Mirage Arena has no multiplayer, and thus also has neither custom D-Links nor any use for friendship commands like Group Curaga over normal Curaga besides story party members.
KH2.5 altered the way Mirage Arena handles player coloration. In addition to Red, Green and Blue, there is a hidden Alpha value for coloring Mirage Arena player models. Additionally, if you import a Birth by Sleep Final Mix PSP save into the PS3 or vice-versa, it will ramp up at least one of the starting RGB values to a previously unknown 199%, which you can change back, and the A value to 50%, which you can't. Barring a creative hex edit of your save file, you will spend the rest of the game's Mirage battles as transparent as a ghost.
The original Japanese menu font characters are present within the English version of the game and have not been upscaled, so importing non-English Patch gamesaves results in a lot of PSP-quality Japanese text. For the same reason, you will have to manually edit the gamesaves to make Finish Commands previously unlocked in Japanese into English again, and those characters use two bits for information instead of 1, as BBSFM uses a version of Shift-JIS to encode all those characters. For accented Latin characters, I've compiled a partial list at viewtopic.php?f=13&t=6059
With all this in mind, it would appear that identifying the significance of several of the save files' Hex values and adding them to Yosh's program would make the conversion process a lot simpler. The source code for version 0.4 is available freely on the net, so with that in mind, I may just code up and compile some updates to the BBSFM Save Editor.
EDIT: I've recently discovered that the same is true of KH2FM; that you can import PS3 saves to the PS2. You need Bruteforce Savedata, Mymc 2.6, either a Hex Editor or PS2 Save Editor, and optionally the KH2.5HD checksum tool.
1. Use Bruteforce to decrypt/encrypt the PS3 saves in the folder BLUS31460-BISLPM66675FM. They'll be named USR-##; with ## being the save's numbered slot.
2. Use Mymc to open a memory card file containing a previous KH2FM save and extract it to a .psu savefile. Backup this file because it will be overridden!
2.5. (Optional) Edit the savefile with a Hex Editor and use the KH2.5HD checksum tool to re-verify the save.
3. Use the Save or Hex editor to isolate the part of the save containing BISLPM-66675FM-## and replace it with the USR-## file. If using Save Editor, rename it to that file before import.
4. Using Mymc, DELETE the save you just exported and reimport the newly modified version you just made. If you try to import it without deleting the original, the import WILL be corrupt.
5. Load the memory card on a PS2 or PCSX2, and you will see your PS3 save in your KH2FM+ saves list in the overridden save's slot.
Warning: If you import a save from a PS2/PSP KH game to the PS3 and use it to gain Trophies that usually require you to first obtain prerequisite trophies before obtaining those Trophies, your game will be flagged by PSN Trophy-tracking sites.
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