Yes. A Christian can become a theistic Satanist. The harder question is what that change would actually mean.
Christian traditions generally place Satan in an adversarial role and direct worship toward God. Theistic Satanism reverses neither of those positions casually: it treats Satan as spiritually real and worthy of devotion. A person moving from one framework to the other is changing a central belief about divinity, authority, worship, and religious identity.
Conversion is not the same as anger
Someone can be angry with a church, disappointed by Christians, or critical of Christian theology without becoming a Satanist. Leaving Christianity also does not automatically point toward any particular next religion.
If your interest in Satanism depends entirely on opposition to something you recently left, give it time. A durable religious commitment should have a positive center of its own.
You do not need to prove anything quickly
There is no Church benefit for making a person convert before they are ready. Read. Ask uncomfortable questions. Compare sources. Keep notes. Visit without joining. If your view changes again, that is information rather than failure.
The Church does not require a dramatic renunciation of family, friends, or former communities as evidence of sincerity. Healthy disagreement and personal boundaries are enough.
What would actually have to change?
At minimum, a theistic Satanist has to mean something religious when speaking about Satan. For this Church, Satan is not merely a symbol of rebellion or a device for criticizing Christianity. Devotion is directed toward a being understood to exist independently of the worshipper.
Practice may then include prayer, meditation, ritual, reading, private devotion, and community. None of those practices needs to be theatrical, expensive, or public.
What about Christian ideas you still carry?
People rarely change entire worldviews overnight. Former Christians may continue to feel fear, guilt, attachment to familiar prayers, affection for parts of Christian culture, or uncertainty about old teachings. Pretending those reactions disappeared usually makes them harder to examine.
Take them seriously without treating every emotion as supernatural evidence. Religious transition can involve theology, family history, habit, identity, and psychology at the same time.
Can someone go back?
Of course. Religious freedom includes the freedom to leave us. A person who later returns to Christianity, becomes atheist, joins another tradition, or simply stops identifying as Satanist does not owe the Church a performance of loyalty.
A better test than “am I converted?”
Ask what you actually believe when no one is watching. Ask whether devotion to Satan has meaning beyond opposition to your former religion. Ask whether the practice makes you more responsible for your choices rather than less.
If the answer is unclear, uncertainty is a legitimate place to remain.