Thanks for the  marionette solution but I would actually need a full search and replace across a whole lot of classes at times not just a prefix.  The above listed find and replace tool for class renaming would be sufficient for my needs and even better if it works for layers too and it is already available, hence my question.   In my case I always add prefixes for imported dwg files, but sometimes I need to change just the prefix, sometimes parts of the rest of the class name (e.g. st