This should cover the basics of UUID change

WARNING: Users with names longer than 15 characters will not be able to
receive money as long as they do not join the server

src/main/java/com/Acrobot/ChestShop/ChestShop.java

@@ -34,6 +34,7 @@ import com.Acrobot.ChestShop.Listeners.ShopRemoval.ShopRemovalLogger;
 import com.Acrobot.ChestShop.Logging.FileFormatter;
 import com.Acrobot.ChestShop.Metadata.ItemDatabase;
 import com.Acrobot.ChestShop.Signs.RestrictedSign;
+import com.Acrobot.ChestShop.UUIDs.UUIDSaver;
 import com.Acrobot.ChestShop.Utils.uName;
 import com.avaje.ebean.EbeanServer;
 import com.lennardf1989.bukkitex.Database;
@@ -88,6 +89,8 @@ public class ChestShop extends JavaPlugin {
         uName.file = loadFile("longName.storage");
         uName.load();
 
+        UUIDSaver.load();
+
         Methods.setPreferred(Properties.PREFERRED_ECONOMY_PLUGIN);
 
         Dependencies.loadPlugins();

src/main/java/com/Acrobot/ChestShop/Listeners/Player/PlayerInteract.java

@@ -10,6 +10,7 @@ import com.Acrobot.ChestShop.Permission;
 import com.Acrobot.ChestShop.Plugins.ChestShop;
 import com.Acrobot.ChestShop.Security;
 import com.Acrobot.ChestShop.Signs.ChestShopSign;
+import com.Acrobot.ChestShop.UUIDs.UUIDSaver;
 import com.Acrobot.ChestShop.Utils.uBlock;
 import com.Acrobot.ChestShop.Utils.uName;
 import org.bukkit.Bukkit;
@@ -115,7 +116,7 @@ public class PlayerInteract implements Listener {
         String prices = sign.getLine(PRICE_LINE);
         String material = sign.getLine(ITEM_LINE);
 
-        String ownerName = uName.getName(name);
+        String ownerName = UUIDSaver.getFullUsername(name);
         OfflinePlayer owner = Bukkit.getOfflinePlayer(ownerName);
 
         Action buy = Properties.REVERSE_BUTTONS ? LEFT_CLICK_BLOCK : RIGHT_CLICK_BLOCK;

src/main/java/com/Acrobot/ChestShop/Listeners/PostTransaction/TransactionMessageSender.java

@@ -6,6 +6,7 @@ import com.Acrobot.ChestShop.Configuration.Messages;
 import com.Acrobot.ChestShop.Configuration.Properties;
 import com.Acrobot.ChestShop.Economy.Economy;
 import com.Acrobot.ChestShop.Events.TransactionEvent;
+import com.Acrobot.ChestShop.UUIDs.UUIDSaver;
 import com.Acrobot.ChestShop.Utils.uName;
 import com.google.common.base.Joiner;
 import org.bukkit.Bukkit;
@@ -15,6 +16,8 @@ import org.bukkit.event.EventPriority;
 import org.bukkit.event.Listener;
 import org.bukkit.inventory.ItemStack;
 
+import java.util.UUID;
+
 /**
  * @author Acrobot
  */
@@ -89,7 +92,7 @@ public class TransactionMessageSender implements Listener {
 
     private static void sendMessageToOwner(String message, TransactionEvent event) {
         String owner = event.getOwner().getName();
-        owner = uName.getName(owner);
+        owner = UUIDSaver.getFullUsername(owner);
 
         Player player = Bukkit.getPlayerExact(owner);
 

src/main/java/com/Acrobot/ChestShop/Listeners/ShopRemoval/ShopRefundListener.java

@@ -7,6 +7,7 @@ import com.Acrobot.ChestShop.Economy.Economy;
 import com.Acrobot.ChestShop.Events.Economy.CurrencyAddEvent;
 import com.Acrobot.ChestShop.Events.ShopDestroyedEvent;
 import com.Acrobot.ChestShop.Permission;
+import com.Acrobot.ChestShop.UUIDs.UUIDSaver;
 import com.Acrobot.ChestShop.Utils.uName;
 import org.bukkit.event.EventHandler;
 import org.bukkit.event.EventPriority;
@@ -29,7 +30,7 @@ public class ShopRefundListener implements Listener {
             return;
         }
 
-        String owner = uName.getName(event.getSign().getLine(NAME_LINE));
+        String owner = UUIDSaver.getFullUsername(event.getSign().getLine(NAME_LINE));
 
         CurrencyAddEvent currencyEvent = new CurrencyAddEvent(BigDecimal.valueOf(refundPrice), owner, event.getSign().getWorld());
         ChestShop.callEvent(currencyEvent);

src/main/java/com/Acrobot/ChestShop/UUIDs/UUIDSaver.java

@@ -64,6 +64,20 @@ public class UUIDSaver {
         return account.getName();
     }
 
+    public static String getFullUsername(String username) {
+        String shortName = NameUtil.stripUsername(username);
+        Account account = null;
+
+        try {
+            account = accounts.queryBuilder().selectColumns("name").where().eq("shortName", shortName).queryForFirst();
+        } catch (SQLException e) {
+            e.printStackTrace();
+            return null;
+        }
+
+        return account.getName();
+    }
+
     public static void storeUsername(Player player) {
         UUID uuid = player.getUniqueId();