Bob,
Many times I have done this and want a clear shot at setting the block up.
I usually do an EDIT COPY. The start a clean drawing and EDIT PASTE-ORIGINAL-LOCATION.
Go to the Layer Command and change the layers as needed. Be sure to Rename the Block to a New Block Name.
If you don't and your try and bring the block back into the same drawing, the existing block will be the layers the block will use and not the ones you did in the new drawing.
But with that said, read the following and you can update the existing block inside your existing drawing as well if you want.
To bring in a block and update existing instances in AutoCAD, use INSERT and select the "Redefine" option when prompted, or use the CLASSICINSERT command. Alternatively, dragging a block from the DesignCenter (ADC) or using BLOCKREPLACE (Express Tool) effectively updates block definitions across the drawing.
Best Methods to Update Blocks
INSERT (Redefine Option):
Type INSERT and browse for the updated source drawing (DWG) containing the block.
If the block exists, AutoCAD will ask if you want to redefine it. Choose "Redefine" to update all instances.
CLASSICINSERT (Simpler Redefinition):
Use CLASSICINSERT to open the old insert dialog, browse, and place the block.
If the name is the same, click "Redefine" to update all existing blocks immediately.
DesignCenter (ADC):
Press Ctrl+2 to open DesignCenter.
Find the file with the updated block.
Right-click the block, choose "Redefine Only" or "Insert and Redefine".
BLOCKREPLACE (Express Tool):
Type BLOCKREPLACE.
Select the old block to be replaced and the new block file.
Key Commands for Block Maintenance
BATTMAN (Block Attribute Manager): Use this if the attributes (text) within the block did not update.
ATTSYNC: Forces all instances to sync with the updated block definition.
REFEDIT: Edits the block directly in the current drawing.
Hope this helps!
Thanks, JRR!