"If a Muslim does not follow the commands of Islam found in plain words in the Koran, is he a Muslim or an infidel?"
Every bit as much as someone who doesn't follow the "Word of God" is a non-believer.
Whole lot of Christians aren't going to make it to heaven based on thou shalt not lie and what they put on their income taxes. :-)
Of course Christians can't even agree on who's going to heaven depending on when they're Baptized.
You responded, "Every bit as much as someone who doesn't follow the "Word of God" is a non-believer."
A Christian who doesn't not follow the law of God and the teaching of Christ is not a Christian.
You avoided the question. Is a Muslim that doesn't follow, or tries to "interpret" away, the commands of his holy book a Muslim or an infidel?
Easy answer:
(A) Muslim
(B) Infidel
Chose one. Islam admits of no middle ground, again by the word of its holy writings.