This program allows you to change the NIDs in a prx/elf.

The program doesn’t check if the code using the NID is correct or not,so,when a NID changed (like with the syscon.prx) the prx will not correctly work,even if you change the NID (using the program).But,this happens just with a few,so with the others it will probably work.

Press X to change the old NIDs to new NIDs from the folder “ms0:/prx”.
Press [] to change new NIDs to old NIDs(ms0:/prx).
Press () to backup your prx’s from “ms0:/prx” to ms0:/prx_BACKUP”,under this option the program tells you the size of the folder.Make sure you have enough space to backup,else the ms will be corrupt.
Press / to exit.

http://forums.qj.net/f-psp-development-forum-11/t-nid-changer-124301.html