Thanks, then I'll try a little later, and I'll say what happened !^^
EDIT : Thanks to Quanno and Segtendo who helped me with the problem of the .rel files !
So thanks to them that I've been able to put a final destination based stage over Shadow Moses, now, I'll try with Robzdablades stages, and I'll tell you how it goes !
EDIT2 : Sorry to say this like that but... IT FU***** WORKED !
I simply renamed my PAL .rel file as the stage I wanted to be replaced, and them I made the manipulation with the hex editor and everything went a lot better than expected !
libertyernie -> Thank you, I used the 75m .rel file, and that was the right one !^^
There is only Grand Stadium that doesn't work !:o
And also thanks to Robzdablades for making those awesome stage !^^