Okay, neither of those mods should cause a melted plug.
The only way you're gonna melt a plug is from pre-ignition and/or a really lean A/F mix in the cylinder. What octane level fuel are you running just out of curiosity? Since these motor's are DI (Direct Injection) they operate at a much higher fuel pressure. You may have an injector issue. This may be one for the service department to check into.