Prepare different plist file, and as VGruenhagen mentioned, use the Preprocessor Macros. You may want to do centralize into something like this:
+(NSString*)plistFileName {
#ifdef _DEV
return @"data_beta.plist";
#elseif _BETA
return @"data_beta.plist";
#else // Release ?
return @"data.plist";
#endif
}