You should base all your Judgements based on divine law, this is mentioned in chapter 5 of the Quran:
Lo! We did reveal the Torah, wherein is guidance and a light, by which the prophets who surrendered (unto Allah) judged the Jews, and the rabbis and the priests (judged) by such of Allah's Scripture as they were bidden to observe, and thereunto were they witnesses. So fear not mankind, but fear Me. And barter not My revelations for a little gain. Whoso judgeth not by that which Allah hath revealed: such are disbelievers. (44) And We prescribed for them therein: The life for the life, and the eye for the eye, and the nose for the nose, and the ear for the ear, and the tooth for the tooth, and for wounds retaliation. But whoso forgoeth it (in the way of charity) it shall be expiation for him. Whoso judgeth not by that which Allah hath revealed: such are wrong-doers. (45) And We caused Jesus, son of Mary, to follow in their footsteps, confirming that which was (revealed) before him in the Torah, and We bestowed on him the Gospel wherein is guidance and a light, confirming that which was (revealed) before it in the Torah - a guidance and an admonition unto those who ward off (evil). (46) Let the People of the Gospel judge by that which Allah hath revealed therein. Whoso judgeth not by that which Allah hath revealed: such are evil-livers. (47) And unto thee have We revealed the Scripture with the truth, confirming whatever Scripture was before it, and a watcher over it. So judge between them by that which Allah hath revealed, and follow not their desires away from the truth which hath come unto thee. For each We have appointed a divine law and a traced-out way. Had Allah willed He could have made you one community. But that He may try you by that which He hath given you (He hath made you as ye are). So vie one with another in good works. Unto Allah ye will all return, and He will then inform you of that wherein ye differ. (48) So judge between them by that which Allah hath revealed, and follow not their desires, but beware of them lest they seduce thee from some part of that which Allah hath revealed unto thee. And if they turn away, then know that Allah's Will is to smite them for some sin of theirs. Lo! many of mankind are evil-livers. (49)
The scripture you follow depends on your religion, but definitely the Quran instructs us not to base our Judgment on law other than divine law.
This probably ansewer part of your question whether you can become a disbelieve by not following divine laws, as this passage is only discussing following divine laws when judging.
But when you know these laws are from God, you should surrender to them even though you think that your way is better, because your creator knows what is best for you. Take for example drinking alcohol, some people say but drinking moderately is better than being too extreme and cutting it out completely, think about seriously, is there such a thing as drinking moderately. Say you have one glass, and you say to you self "I'm not drunk", then after you have had a few more, etc... until your too drunk to tell if you are drunk or not drunk.