Riot Games' Vanguard anti-cheat system can detect unauthorized modifications to game files. While some tools claim to be "undetected," using any software that alters game memory or data can lead to a permanent account ban.
Most modern skin changers for League of Legends rely on specific frameworks: How to Install LoL Custom Skins (Tutorial)
Game updates frequently break these tools. Using an outdated version can cause the game client to crash or lead to immediate detection. How They Work
Many "free" skin changers are bundled with malware , keyloggers, or other malicious code designed to steal login credentials or personal data.