Changing default sounds and 'skull' icon

not at the current time, tho you can as you suggest change them .. this only effects your installation and not those of the clients connected to you..

 

Sound Changes
If you replace all your sounds in /res/wav simply make sure the new sounds are titled exactly the same as:
attack.wav
cancel.wav
castSpell.wav
chat.wav
creatureDeath.wav
dice.wav
dice1.wav
dice2.wav
dice3.wav
dieCreature.wav
freeMode.wav
healDamage.wav
initMode.wav
killCreature.wav
logOff.wav
logOn.wav
movement.wav
newInit.wav
nextInit.wav
possibleCrit.wav
takeDamage.wav

If you want to share your sounds with your players, please distribute the wav files and have them replace the sounds too. Just make sure to keep a backup of both sound types

Status Icon Changes
Yes and no. The no = standard users. The yes= adventurous users... You could if you change the jar file to zip, then extract, then find .com.mindgene.images.status then change the png for death1.png , disabled.png , and dying2.png (each 200px x 200px)then rezip, then rename the file extension back to jar. Of course I would create a backup just in case.

Remember this will only change the way you see things. You'll have to distribute the new jar to your players if you want them to see also.