I just tried a test drawing to simulate this. 4 layers: 0, chassis, drilling pattern & objects.
An object block was created, putting the outline on the "objects" layer and the drilling pattern on the "drilling pattern" layer. Everything was set to "bylayer".
A simple chassis outline was drawn on the "chassis" layer and 4 insertions of the object block made on layer 0. The layer attribute of one insertion were then changed to "chassis" just to see what would happen.
As expected, switching off the "objects" and "drilling pattern" layers turned off just those items. Turning off 0 switched off the 3 blocks on that layer. Turning off "chassis" also turned off all of the changed block, but I expected that.
It was possible to change colours of the insertions as a whole by changing the layer colours but not individual insertions. I also expected this. The same applied to linetypes.
As I use Autocad at work, this behaviour seems perfectly ok. However, exploding a block doesn't dump the bits of block onto layer 0. I find that preferable to Autocad's way.
If anyone would like me to try anything else on this, just post here.
This is on the community version of Qcad.