This should work:
public static inline var DATA_COMPLETE_LEVELS = "save_game_data_complete_levels";
public var completedLevelKeys(get, set) : Vector<String>;
function get_completedLevelKeys() : Vector<String>
return Reflect.field(this.data, DATA_COMPLETE_LEVELS);
function set_completedLevelKeys(values : Vector<String>) : Vector<String>
{
if(null != values)
Reflect.setField(this.data, DATA_COMPLETE_LEVELS, values);
return values;
}