Commands are enclosed in ACMD() functions. While I wouldn't say you could typically add a new command anywhere in atcommand.c, you can add a new command before or after these functions.
Example:
ACMD(searchstore){ int val = atoi(message); switch( val ) { case 0://EFFECTTYPE_NORMAL case 1://EFFECTTYPE_CASH break; default: val = 0; break; } searchstore->open(sd, 99, val); return true;}ACMD(mynewcommand){//...}
Thank you sir!