How to disable/enable schedule job and keep run_count?

You enable one or more jobs by using the ENABLE procedure or Enterprise Manager.

The effect of using this procedure is that the job will now be picked up by the
job coordinator for processing.
Jobs are created disabled by default, so you need to enable them before they
can run.
When a job is enabled, a validity check is performed. If the check fails, the
job is not enabled.

For more information refer to the link

http://download.oracle.com/docs/cd/B19306_01/server.102/b14231/scheduse.
htm#sthref3569 ==> ( see Enabling Jobs and Disabling Jobs)

Regarding run_count please refer to the following metalink article:

Article-ID: Note 602729.1
Title: Mismatch in RUN_COUNT of DBA_SCHEDULER_JOBS