This paper considers the problem of dynamical order assignment for linear descriptor systems by derivative feedback control. The approach is based on an ability to adjust the number of infinite non-dynamical modes of the system within a permissible range. Increasing the dynamical order enables the designer to implement specific otherwise unrealizable control strategies. On the other hand, dynamical order reduction simplifies the design procedures for a large scale system. The solution is obtained by imbedding the descriptor-space problem in an equivalent state-space problem where a zero-value eigenvalue with a prescribed geometric multiplicity is assigned to a linear state system by proportional feedback control