In the standard application, the "Lives" counter is stored as an integer value (usually 5). When a life is lost, the value decreases by 1. The mod likely utilizes Hexadecimal editing to freeze this integer value.
King Entertainment (now a subsidiary of Activision Blizzard) aggressively pursues DMCA takedowns of modded APKs. Why? Candy Crush Soda Saga v1.0.0 Mod -Unlimited Lives-
Disclaimer: Modifying games violates King's Terms of Service. This is for educational archival purposes. In the standard application, the "Lives" counter is