You can customize your Jobspec Presets field to change the default behavior on a submit.
The standard Jobspec Presets field looks like:
To disable Job Closure, make this change:
Status open, fix/same
This will change the default behavior of p4 fix, p4 change, and p4 submit to leave job status unchanged for any open job when submitting a changelist. Notice the use the special fixStatus of same. Other fixStatus's can be created and used, see the System Administrators manual Jobspec section for more information about fixStatus's.
Additional customization around Job fix behavior can be provided by custom "fix triggers" as documented in the System Administrator's guide "Scripting Perforce" section.