The free LISP utility LayNsel (see www.cadstudio.cz/download) selects and moves blocks and other objects to a specified layer.
After you load the LayNsel.vlx file and start the LAYNSEL command, first pick an entity to select its layer (it can be also nested in a block). Then either press Enter to manually select objects to move to that layer or press "B" to automatically select all blocks (block references, inserts) containing the specified layer and move them to that layer.
Please note that only the INSERT will be placed on that layer, the individual entities in the block definition won't be changed (you can use SETBYLAYER for this).
If you want to perform another operation with the selected blocks, use the "P" (previous) selection mode in your subsequent editing command.