update the doc to emphasize that it is required to do re-indexing

docs/docs/PreviewFeatures.md

@@ -67,6 +67,8 @@ is set by the Partition Service. Here is an example to enable this feature by se
 
 If the property "custom-index-analyzer-enabled" is not created or the property value is set to "false" (String type) in the
 given data partition, the default index analyzer will be applied to indexing and search.
+
+After the feature is enabled, **it will require re-indexing kinds in the given partition in oder to adopt the custom analyzer.**
  
 
 ## Index AsIngestedCoordinates

indexer-core/src/main/java/org/opengroup/osdu/indexer/service/IndicesServiceImpl.java

@@ -215,8 +215,7 @@ public class IndicesServiceImpl implements IndicesService {
     }
 
     private IndexSettingsAnalysis getCustomAnalyzer() {
-        List<String> mappings = List.of("_=>\\u0020");
-        MappingCharFilter mappingCharFilter = new MappingCharFilter.Builder().mappings(mappings).build();
+        MappingCharFilter mappingCharFilter = new MappingCharFilter.Builder().mappings("_=>\\u0020").build();
         PatternReplaceCharFilter patternReplaceCharFilter = new PatternReplaceCharFilter.Builder().pattern("(\\D)\\.|\\.(?=\\D)").replacement("$1 ").build();
 
         Map<String, CharFilter> charFilterMap = new HashMap<>();