It is quite painful to discover that a few-day long job is going to be prematurely killed due to an error in setting walltime limit for it.
Is there a way to change it for a running PBS job?
old question, but I'm adding some additional information for anyone that lands here from Google
Note that once a job is running in TORQUE, any request to lengthen the walltime will be ignored unless the qalter command is executed by a TORQUE manager or operator. To extend the walltime of a running job, you must contact an administrator. You can shorten the walltime of your own running jobs, and if your job is not running (queued or held) you can increase the walltime with qalter.