Detect/handle parsing error and log format change

Hi, I have been asked about log parsing and parser error detection in Splunk. The questions are: In general - how can and should I detect parsing errors in Splunk? (New version of log source, etc without notification to Splunk admin, etc) - how should I handle the new log format? There are already data in the index with the old source type. If I modify the sourcetype definitions, it will break the search time field extraction, is it? Clone and modify the source type? I don't find a guide or best practice in the docs... Thanks, István