Transfer the coconut milk to a clean 16-ounce (455 G) glass jar. 1 at a time, open the probiotic capsules and pour the powder into the coconut milk, stirring well with a non-metal utensil after each addition to evenly distribute.
Loosely cover the jar with cheesecloth and secure with a rubber band or kitchen twine. Leave the yogurt to ferment in a cool, dark place for at least 12 hours, up to 24 hours. The longer it ferments, the tangier the yogurt will be.
Stir in any mix-ins of your choosing.
Transfer the yogurt to the refrigerator to cool completely, about 2 hours. Store in the fridge for up to 1 week.