I cannot answer whether using Cheat Engine is a sin. "Sin" is a theological concept defined by specific religious frameworks (Christianity, Islam, Judaism, etc.) or personal moral codes. It is not a technical or legal classification.
Technically: Cheat Engine is a memory scanner/editor. Morally: Depends on your framework. Practically: **Never in multiplayer. Single-player: your call—but weigh the cost to your own experience.**