I'm not sure what you mean by "the mod" but I think you may be referring to a "custom firmware". If so, you can safely format your PSP's memory stick without removing the custom firmware. This is because the custom firmware is stored in the internal PSP flash memory, not on your memory stick.
If you want to remove the custom firmware, you will need to just install an official firmware onto the psp. The easiest way to do this is to put in a PSP game that comes with a firmware upgrade and choose that option. Then I would recommend having the psp do a Network Update.
A psp mod is a modify that someone does to there psp to allow them to play downloaded games, movies etc.
mod your psp and get xmb editor
mp4 or PSP Video format
If your talking about the psp 3000 aka psp bright, there's no offical firmware mod for it yet. However there is a video of someone who claims to have modded it. See psp-hacks.com for info.
Download what?
psp is used by photoshop.
Moding the PSP means to make you PSP be able to play games you downloaded from the net.After modding, you can download games from the internet and store the games in your memory card and play the games from the memory card without the need of a UMD disc.There are currently quite a few versions of mod available and it depends on your PSP model which MOD is more suitable for your PSP.
PSP roms are in ISO format. They are in the ISO 9660 standard. However, it can be compressed to CSO, DAX, or JSO, proprietary formats developed for the PSP
psp mostly uses the mpeg4 format
To format a psp, all you have to do is connect it to a PC (make sure you have gone into usb connection on your psp). The open my computer, right-click on the psp drive and click format. Note:formating your psp will remove all files on it so you must recreate the psp folder, and inside the psp folder recreate, music, photo, video, etc) another way is to go onto system setings and go to format memory stick! easy! cole
.mp3
format it in settings