Objective-Cの正規表現、キャプチャした変数で文字列置換 ref: http://qiita.com/AyatoKinkori@github/items/750af1bcade414f4effc

replace_capturestr.m

NSString *str = @"hogehogefugao";
NSRegularExpression *regexp = [NSRegularExpression regularExpressionWithPattern:@"(hoge).+(fugao)" options:0 error:nil];
NSString *new_str = [regexp
              stringByReplacingMatchesInString:str options:0 range:NSMakeRange(0, str.length) withTemplate:@"$1山$2"];
//new_strは hoge山fugaoになります。