If Era is still using ganis like era_swift-piano-play1.gani for the piano the script can be modified to check for a client flag. I.e.
PHP Code:
SCRIPT
if ((created || playerenters) && !client.option_instruments_muted) {
for (temp.i = 0; i < 6; i ++) {
if (params[i] != null) {
play(params[i]);
}
}
}
SCRIPTEND
Which will allow players to mute instruments for just themselves.