I'm not very familiar with hex editing but the way we edit rosters is with the madden editor. The way I learned how to edit rosters was by following the links below and lots of trial and error.
http://www.operationsports.com/forum...editor-v1.html
First thing I can recommend is to read the first post on this thread above you will need the software mentioned in it. If you have an XBOX follow that thread exclusively. But if you have a PS3 ignore the part about Horizon. Don't be intimidated if you have never done this before the worst thing that could happen is you screw up a roster file. So, just make sure you play around with roster files you don't mind messing up, until you get the hang of it. The first time I did this, I loaded the roster file back onto my console and no players were found, on any team, period. I was freaking out, I thought I erased all the players on the disc and had to buy a new one. Now I know it's pretty much impossible for me to erase the actual game data on the disc.
If you have a ps3 you will also need bruteforce software to encrypt and decrypt ps3 files, so you would use it in place of horizon. Follow the link below to find out how to download and use bruteforce. The first post in the thread will tell you.
http://www.operationsports.com/forum...ditor-ps3.html
If you really like editing rosters this will be well worth the time you put into it. As far as adding your own custom photos off the internet or something, I don't know of a way to do that, some people have tried to no avail. The photos we have to work with are what EA has loaded on the disc.