In molecular communication systems operating in a crowded biochemical environment, there is the potential for unintended chemical or physical interactions with external biochemical systems. In order to avoid these interactions, or ensure coexistence, it is necessary to tailor the signaling scheme. In this paper, we propose a signaling strategy exploiting chemical reactions between different transmitted chemical species. While intuitively appealing, the non-linear nature of the governing partial differential equations (PDE) means that selecting the signaling strategy to minimize the probability of error is com-putationally challenging. To reduce this computational burden, we introduce a new proxy metric called the modified signal-to-interference difference (mSID). We show that optimizing the mSID yields low complexity and near-optimal solutions, requiring only deterministic nonlinear programming rather than standard brute force Monte Carlo methods.