Well, I am quite happy about the results. The peg on the XN Raiser perfectly fits on RG 00 Raiser's backpack.
Since I only have one RG Raiser for now, I tested it on my RG 00 Gundam Seven Sword/G's back pack.
Aaaanddd, voilà! there we have it, no snap fit problems, it seem like it was also made for RG Raiser.
Will test if it would fit with RG 0 Raiser.