Are we allowed to change the portions of inheritance assigned by Islam according to our preferences?

Concerning the portions of inheritance assigned to each heir in the Holy Quran, Allah Almighty has said:

These are the limits set by Allah.

(Surah an-Nisa’, 4:14)

Changing these portions according to our preference is not permitted (Surah an-Nisa’, 4:15).

It is not correct to write a will in favor of a heir, except that a husband writes a will for the residence of his wife, in fact, writing such a will is necessary for him.

(Fiqh Ahmadiyya, vol. 2, p. 118)