If you mix it yourself, you know exactly what is in it.
This means you can vary/substitute ingredients such as heart salt for regular salt if you're on a DASH diet (half the sodium chloride is replaced with potassium chloride).
You can't swap arbitrarily but it's also not like the baking ingredients are the input to a pseudo random number generator that selects the result. You can absolutely make it more/less sweet, more/less chocolatey, more/less moist, add hints of different flavors etc.
This means you can vary/substitute ingredients such as heart salt for regular salt if you're on a DASH diet (half the sodium chloride is replaced with potassium chloride).