The beauty of our hobby is the freedom of choice and the creativity that it allows for. There are styles that have windows of opportunity, and then there are variations of style, and then there is sheer creativity or as I've often heard it referred to as "No Pants brewing".
I like to use crystal malt in varying amounts to achieve or target a flavor, and depending on the target/variation of a specific style that I'm shooting for, and through trial and error I've learned how much of a given specialty malt I need to add in order to achieve that targeted flavor. In other words, design a recipe and then tweak it to your targeted taste. No rules, no boundaries, only creativity and experimentation will satisfy ones aspirations.