couldn't change the line weight of resistors, or change their color

[SLW210]

I believe in 2005 you should be able to set a block to ByLayer. As already mentioned use refedit or explode the block and recreate it. Pretty sure 2005 has inplace refedit and if you do some googleing you could probably find a video on how to type in commands.

[ReMark]

Yes, 2005 has in-place editing of xrefs and blocks. The topic is fully covered in the Help file.

[SLW210]

[ATTACH]25740[/ATTACH]

 

Maybe this will Help(F1)

[eldon]

Another slightly larger picture taken from 2005

 

[KiLLiNG-TiME]

Why not just set ucs to world wblock your blocks out into a folder, open each one up, & sort out the layers colours etc, then you will have a master set of your drawings (your blocks) that you can then insert back into your drawing redefining the blocks as you go.