The combination of coordinated multi-point (CoMP) and underlay spectrum sharing promises substantial spectral efficiency (SE) gains for future cellular networks. However, this concept has been largely overlooked in the literature. Moreover, none of the few relevant studies consider the use of »standard» transmission strategies to facilitate the adoption of the aforementioned communication paradigm by 5G networks. The use of load-controlled antenna arrays (LC-AA) and symbol-level (SL) precoding can further enhance the performance of CoMP cellular networks, as it has been shown in the literature. Nevertheless, the corresponding research works do not consider a spectrum sharing setup. In this paper, we fill this gap in the literature by deriving the optimal power allocation strategy (in the sum-SE sense) and the corresponding algorithm that implements this solution for scenarios where various linear or SL precoding schemes are applied. Numerical simulations indicate the feasibility of the proposed approach for LC-AA-equipped CoMP networks and shed light on the effect of various parameters on system performance.