Q: Can a Christian be a magician?
A: It depends what you mean by a magician. A magician is kind of a vague term since it could mean several things such as witchcraft, sorcerer, wizard, black magic, white magic, entertainer, etc. I just call it illusionist for better simplification, but it all depends on your intentions.
The whole chapter of (Romans 14) talks about the diversity among Christians which we can also use for this question since it speaks about subjective sin. Subjective sins are things that are not really sinful according to the Word of God, but people make them sinful anyway because is not just what you do, is also the purpose why you are doing them (Romans 14:20-23).
(Romans 14:23) says: EVERYTHING that does not come from faith is sin.
In other words, been an illusionist could be or not be sinful depending on the conviction that you have in your heart, but know this (1 Corinthians 10:31): whatever you do, do it all for the glory of God.