For the sake of definition: The LINES parameter is an optional parameter on the JOB statement for use with ESA 4.2 and later releases. It indicates the maximum amount of output, in thousands of lines, to be printed for the job's sysout data sets. It can also be used to specify the action that the system is to take if the maximum is exceeded.
But if you say
Can we put in LINES=(999999,WARNING) and would the job still run fine if it exceeds 999,999,000 lines of ouput ?
Just don't do that unless you are serious about that your site support group should kill you and hid your body ....
Site limits are established after careful consideration of the ramifications and changing them may cause unexpected side effects. As for example, if you start writing millions of lines of output to the JES spool, sooner or later it fills up. When the JES spool fills up, JES stops submitting jobs and even worse, sometimes jobs stop running, until the spool free space hits a certain percentage. Spool space is also needed to sign onto TSO so nobody can get into TSO until spool space is freed up ... and so on..so forth... beware.