Need Help Of Replace Files On Xgd3 Iso, replace files on XGD3 iso Options

[dogkarl]

I am a xbox360 modder. I localised a lot of xbox360 games to my native language. I usually done this by modify the files on xbox360 iso, sometimes the file I replaced is bigger than the original file, so I created a tool to rearrange some files on iso to squeeze in the new file.
The tool works generally well, but in some cases, the new iso can't be read by xbox360.
So, I really appreciate if somebody can shed some light on the format of xbox360 XGD2 XGD3 iso.

First, of the file system of xiso, what elements can not be modified? For example, the root position or xex file position?
Second, if the iso is in XGD2 format ,and if modified properly, the modified iso can be installed on hard disk, but since XGD3 format is introduced, the modified iso can not be installed on hard disk anymore(but the game still runs well). I guess this is because there are block hashs somewhere on XGD3, but I don't know for sure. Maybe you can give me some suggestion?
Also if someone can tell me who I should ask about this kind of questions,please help. Thanks.