There is a saying in dance “learn the rules like a pro, and then break them”.
It’s perfectly appropriate for singing as well.
Freedom to express yourself is directly related to the amount of control you have over your voice. With good singing technique, you have equal control of your high, middle and low registers. You are essentially creating a baseline that you should always return when warming up and vocalizing.
Does this mean you have to stay there? Absolutely not. Once balanced, the voice can explore the qualities that ring true with the style of music you want to sing.
Although good singing technique is necessary to sing all styles of music well, certain styles can require the voice to do certain unique co-ordinations, especially with vowel formation, amount of breath being released, glottal attack and twang. However, most important is knowing that you are mixing well from the top of your range to the bottom.
Get your voice balanced and then start to build the qualities you are looking for.