Short answer: you can’t.
Longer answer: a style in darktable is just a collection of modules applied, with a certain set of parameters defined in each one. It’s not different from applying the same modules with the same parameters by hand, the style is just a shortcut to do it with a single click. The only way to ‘moderate’ the effect of the style is what you’re doing: go into each module and retouch its parameters to tone down its effects. Some modules may need to change the opacity, some others the strength of some parameter, others may even not need to be touched. The good thing is that once you find the right set of modifications you can save a new style named ‘Some style - reduced’ and use it from then on.