If I purchased a feature, will I pay for it again?

The answer is: No.

You will be able to download your purchase again for free. You purchase the feature once.

If you lose your In-App Purchases because your app was accidentally deleted or you had to restore your device without a backup, or you got it on iPhone and installing the app on iPad.

To download your In-App Purchase again, you must download it from within the installed app using the same iTunes Store account name you used for the original In-App Purchase.