For those that have multiple external HDDs connected to your PS3 and are using the gameData.pkg (released a few weeks ago) this tool (tweak) may be helpful to you, so you don't have to be swapping USBs in order for the gameDATA app to see your current external HDD as the (1) main ext HDD. So for those that have been enjoying the latest PSN DUPLEX backup games, but running out of internal HDD space, plus those that have more than one external HDD (and don't wish to be swapping the external HDDs so they can be identified as the (1) USB drive, this will help you.


You will need:
EXT GAME DATA LOADER- Download
multiMAN- Download
gameDATA.pkg- Download

know how to use multiMAN's file manager or using FTP to transfer a folder.
more than one external HDD--if you have only one external HDD--they you don't need to bother using this--unless you tend to use a USB stick every now and then to install small files to your PS3.

[SPOILER="Installation Instructions"]Download the RAR file below called: EXT_GAME_DATA_LOADER_BY_JAY-JAY.
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Extract the RAR file until you have a folder named: EXT_GAME_DATA_LOADER_BY_JAY-JAY
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Inside that folder get and copy the folder called: 000_EGDL00001-(EXTERNAL GAME DATA LOADER) to your external HDD's GAMES or GAMEZ folder (using either multiMAN's File Manager or FTP)
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If you have more than one external HDD and you plan on installing PSN Games and etc (like those that are enjoying the DUPLEX releases) than copy this folder to your other external HDDs.
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Copy the game cover named: EGDL00001.JPG to multiMAN's game covers directory: /dev_hdd0/game/BLES80608/USRDIR/covers/ -- you will find this game cover image inside: EXT_GAME_DATA_LOADER_BY_JAY-JAY folder.
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copy gameDATA.pkg to any external HDD or USB stick (Don't install yet, please continue with the instructions below until I instruct you to).
Note 1: you will only use this tool in order to exit EXT GAME DATA LOADER mode, so you can go back to multiMAN and load other games and etc. You will not have to use this tool to turn on EXT GAME DATA Mode--since this tool only points to whatever external HDD is listed as your USB 000 or USB 001 HDD.
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Note 2: If you don't install this tool, then you will have to restart your PS3 in order to exit this mode.
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Now launch multiMAN. And do a rescan (REFRESH LIST) for your game list so it reads your external HDDs for the new game title called: EXT GAME DATA LOADER.
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If you installed more than once this game title to your multiple external HDDs than you will have more than one. This is normal.
What I did after this, was I renamed the game title (using multiMAN's RENAME feature) so it would say which USB HDD it would apply to.
For example: I have three external HDDs and I copied this folder to each of their GAMES directory. So I then renamed each game title in multiman as:
001 EXT GAME DATA LOADER (USB 01)
002 EXT GAME DATA LOADER (USB 02)
003 EXT GAME DATA LOADER (USB 03)
--by default the game title is called: 002 EXT GAME DATA LOADER (USB 02) -- you must rename these so you can understand which external HDDs you want to load using the EXT GAME DATA mode to.
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Now after you renamed them, proceed in going into the game menu of multiMAN for each game title you have installed on your external HDDs. Then make sure to check (enable) the EXT GAME DATA feature for each one. Once you do this, simple press O to return to the game directory in multiMAN and then just launch the title--like you do when you launch a game in multiMAN.
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Once you return to the XMB (you should be in EXT GAME DATA mode (you will know this is true because all your game XMB icons will be grayed out (like ghost images--and they won't launch). Don't panic! This is normal.
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Now go ahead and install gameDATA.pkg--You will need to do this installation to each external HDD you have connected to your PS3--meaning that you will need to go into multiMAN and launch each different EXT GAME DATA title that is associated with each external HDD in order to install it on that drive.
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Now after installing the pkg, just ignore it for now and go ahead and either install a PSN game to that external HDD or play a PSN game (or any other homebrew that can be installed in the XMB).
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Once you are done playing that game, then find the Game DATA Mode icon (the one that you just installed) and launch it twice from the XMB and your PS3 will be back to normal mode. -- you must run this tool once or twice--you will know when you are back to normal XMB mode when you see multiMan's icon in your game XMB menu back to normal.

Memo:
To devs: Hopefully a dev will make this easier for us.
To super-noobs: Please don't panic when you are in USB mode and you see all your xmb icons look like "ghost" images. This is NORMAL when you are in USB mode. Only those PSN games or homebrew apps that you have installed to that particular External HDD will show their icons as normal. SO PLEASE DON'T PANIC.
To everyone: Do not try to run the "dummy" game on the XMB called ***EXT GAME DATA LOADER (USB***)--that will not load. OK.[/SPOILER]

Source- psx-scene