[Grace]

Yes, he can change the Constitution, with the approval of the National Council, but to include Alex, he would have to include all not-legitimate heirs, thus opening the way for other potential kids (for example Jazmine Grace if the rumors were true...)
I guess he might want to change the law if he developed a wonderful relationship with Alex (and his mother), and if things got rough with Caro and or her kids, but at present, giving his "difficult" relationship with both Nicole and baby, it is not very probable.

Kisses

Eta: Adoption is not an option anymore under the new Constitution; so the line at present is Caro, Andrea, Pierre, Char, Alex, Steph, Louis, Pauline...