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. strip/rename project or location specific parts, or if e.g. Phase3 in a class names needs to changes to Phase4 etc.).   And it would be almost heaven if this find/replace could be invoked when duplicating an entire series of classes (e.g. all 15 Phase3 classes to be duplicated for an e.g Phase5 and then at the same time rename Phase3 to Phase5 in one go).   It is something I run into quite often as things get added and added and changed and changed again all the time and often for a whole range of classes. (e.g. Scope A becomes Scope C, or split into Scope C and Scope D and I need to adjust/duplicate class names to reflect the changes (or when it gets reverted back and some classes need to be merged back into the previous configuration).   So a good and flexible find/replace for class and layer names would be quite useful. I guess there are more people who have similar situations/needs.