I've got a drawing of a city map containing street lights as blocks.  My goal is to assign a number to each pole.  My first thought was create a new block with an attribute and then simply replace all the others with the new one.  Seems I can't replace a block with a block that has attributes.  Anyone have a suggestion as to how I can accomplish what I'm after?  Thanks in advance!

After searching around, let me rephrase this.  Apparently this may have been imported from another program way back when.  So for these street light blocks, I really have about 800 of the same blocks named ST_1 through ST_800.  This drawing just seems to need cleaned up, greatly!  It's the same case for other blocks, such as fire hydrants, water valves, pole lights, sewer drains...etc.!  Anyone help?  It seems like it may be a very time consuming fix having to go one by one

Sounds like a task best suited to a custom lisp program.  Question is, does ZwCAD support lisp?

Yes, it does. I run a few already.

There is no problem with replacing blocks with attributes in AutoCAD. You can then use our InsertC/BlockC utility (see Download) to automatically renumber the blocks (fill their attributes).