UMDGen v2.00 lets you open up the files on a UMD and edit them. Then you can save the UMD as a file called an ISO so you can play the game but play it with whatever you edited. But first you would have to change the ISO into a CSO and then place it under your iso folder which is in the root of your memory stick. To do that you easily compress and decompress the iso, cso or possibly dax with a program that can do so. I use YACC(Yet Another CSO Complier) which I will provide here. =)
UMDGen Download Link -
http://www.sendspace.com/file/cowigg
password - codinghs.com
YACC -
http://www.sendspace.com/file/vrrb0k
password - codinghs.com