A ForcedLevelPatch is always executed against level.dat, (no matter what patchLevel is set for a world)

src/main/java/ru/bclib/api/datafixer/ForcedLevelPatch.java

@@ -0,0 +1,47 @@
+package ru.bclib.api.datafixer;
+
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.ListTag;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+
+/**
+ * A Patch for level.dat that is always executed no matter what Patchlevel is set in a world.
+ */
+public abstract class ForcedLevelPatch extends Patch {
+	protected ForcedLevelPatch(@NotNull String modID, String version) {
+		super(modID, version, true);
+	}
+	
+	@Override
+	public final Map<String, String> getIDReplacements() {
+		return new HashMap<String, String>();
+	}
+	
+	@Override
+	public final PatchFunction<CompoundTag, Boolean> getWorldDataPatcher() { return null; }
+	
+	@Override
+	public final PatchBiFunction<ListTag, ListTag, Boolean> getBlockStatePatcher() { return null; }
+	
+	@Override
+	public final List<String> getWorldDataIDPaths() {
+		return null;
+	}
+	
+	@Override
+	public PatchFunction<CompoundTag, Boolean> getLevelDatPatcher() { return this::runLevelDatPatch; }
+	
+	/**
+	 * Called with the contents of level.dat in {@Code root}
+	 * @param root The contents of level.dat
+	 * @param profile The active migration profile
+	 * @return true, if the run did change the contents of root
+	 */
+	abstract protected Boolean runLevelDatPatch(CompoundTag root, MigrationProfile profile);
+}
+