Can a person write a will calling for his assets to be distributed after his passing in a different manner than that prescribed by the Torah?
According to Torah law, ownership over a person's assets is transferred automatically after his passing to his family members in the sequence stipulated by Halacha. This automatic transfer of assets does not depend upon the deceased's wishes, and thus a person cannot instruct that his estate be distributed differently. One may, however, write a will calling for the distribution of his assets in the form of gifts given before his death, rather than as an inheritance. Meaning, the will must stipulate that the assets are distributed during his lifetime, and not after his death. Clearly, a person can distribute his property during his lifetime however he wishes. Therefore, although a person cannot override the Torah's laws of inheritance, he can circumvent them by writing a legal document calling for his assets' distribution before his death.
Writing a will in this manner gives rise to a number of Halachic issues; it is therefore imperative that a person who writes a will does so in consultation with a competent Halachic expert so as to ensure that it is formulated properly.
Despite this provision allowing a person to distribute his assets as he wishes, it is nevertheless a Mitzva to distribute at least some of one's assets in accordance with the Torah's laws of inheritance. The story is told of the renowned Sadik David Sion Laniado Z"L, who wrote a will whereby all his assets were donated after his death to charitable causes. However, he left over one Lira (the unit of Israeli currency at the time) that would be inherited by his children in accordance with the Torah's laws. Thus, although Halacha allows a person to write a will that circumvents the Torah's inheritance laws, it is nevertheless proper to see to it that at least some assets are transferred to one's heirs according to the Torah's system of inheritance.
Summary: If a person who wishes for his assets to be distributed after his death in a different manner than that prescribed by the Torah, he may write a will whereby the desired distribution takes effect before his death. One who wishes to write such a will must do so in consultation with a competent Halachic authority. It is proper to leave aside at least some assets to be distributed among one's heirs in accordance with the Torah's inheritance laws.
See the book- "Pure Money" by Dayan Cohen, pages 231-232.
