If you want to rename all your layers, blocks or other AutoCAD drawing symbols by adding a common prefix or suffix, you can use the free PSrename utility.
The PSrename command allows to select the symbol table (Block, Dimstyle, Layer, Linetype, Style, Ucs, View) and to enter an arbitrary prefix or suffix string. Then it renames all selected symbols (e.g. layers) by adding this prefix or suffix string. It automatically skips renaming "protected" DWG symbols like the layers "0" or "DEFPOINTS", "AVE_RENDER" blocks, xref symbols, etc.
You can download PSrename from www.cadstudio.cz/download, load it with APPLOAD.