You can use a layer key to map specific entities within a block to a layer in the drawing into which the block is inserted. For example, the millwork blocks (see About Collecting Similar Blocks) have the hatch entity assigned to the layer “HATCH.” If the Recipe Specification (XML file) that references this block library has the attribute “remapLayers” set to true, as shown below, then any layer that matches a layer key in the current drawing will be replaced with the layer that is assigned to that layer key. In the case of a drawing using the standard AutoCAD Architecture template file, in which the HATCH layer key is mapped to the AecDtl-Patt layer, any block library entities that were assigned to the HATCH layer will end up on the AecDtl-Patt layer when inserted into the drawing.
<AcadBlockProps><BlockName dwgLib="dwgs/AecDtlLib_WoodMillwork.dwg" remapLayers=”true”>AecDtl_millworkBlk1</BlockName> <Scale>6.0</Scale></AcadBlockProps>