Rest easy knowing your purchases are safe - Apple keeps careful track of them all and will never double charge you for what you previously bought (either the app, or the in-app purchases). If you go back to the "Browse" tab in Lightbow, and navigate to any previous purchase, you should see both an "Add" button (to make a link to the whole collection from your Presets list) or "+" buttons next to each preset (if you want just one or more specific presets in your Presets list). If you delete Lightbow from your iPhone, it will indeed do what the alert panel says about deleting local content, and the next time you reinstall, your Presets list resets to the factory defaults. Don't despair—just re-add links to whatever favorites you have.
Having an issue after a re-install where something appears locked that you know you previously purchased? This is an easy fix, and applies to any other app as well. Sounds like you need to ask the App Store to refresh your receipt! First, please make sure that you're signed into the same app store account across all of your devices. Go to the Settings app, and under "iTunes and App Stores" make sure your devices show the same Apple ID. Then return to the Lightbow app and tap the "Restore Purchases" button at the bottom of your Settings tab. Hopefully that will do the trick, but if you still receive an error message please let us know what it says so we can further assist you.