I have combined 2C-B and mushrooms and although it wasn't the best combination I tried, I am pretty sure it's not dangerous. Miprocin is very similar to psilocin, the plus side is that it shouldn't matter too much regarding safety if you add it as well but the potential downside may be that it is slightly redundant.
Always dial down dosages when you combine drugs, the effect is additive even if not linearly. There may be subjective synergy which happens especially when the drugs work on the same receptors (true here) and if nothing else, having drugs in your body may occupy your metabolic systems from being able to break down extra added drugs as fast. This is especially true when the drugs are broken down by the same enzymes (AFAIK not entirely, but perhaps partially true here).