Not as decoration, but a lot definitively put in in the filter named activated carbon, that is actualy charcoal from different wood types. Mainly Bamboo or Coconut shell.
The wood chips are burned than steam activated with nitrogen and co² gass under pressure. Some people leave deactivated carbon in the filter as biomedia. I guess it can be used indefinitely, Charcoal stays Charcoal if its not under huge pressure, next step it turns into (rock) Coal, later and deeper it form Anthracite (Hard rock Coal), than Graphite and finaly Diamond.
But indeed as Keith mentions heating up wood will have the same effect as boiling it.. Than it changes on a cellular level, the Cellulose structure will be damaged and it becomes softer and will decay sooner. Some say you need to cook wood to desinfect it and get the tannins out, others say not nessecary water changes get the tannins out as well. I belong to the later, personaly i also never encountered an infected piece of wood.
Anyway, back to burning it, as said it distroyes the structure and when you do not charcoal it all the way through it will water log and the damaged still wood layer under the burnmark will decay sooner and probably shed off in time. But that is a guess, i never tried..
Patience does the job as well.. Spiderwood is very light colored, initialy it turns gray with biofilm when submersed, but in time it will go darker so dark in the end it will be almost black. I actualy forgot how long it took, but in my tank it did.