Yes, you can. If you have locked jobs that you wish to unlock under your subscription plan, you can use the button "Add this job to your plan". This button will unlock your job and will make it part of your active jobs quota, just as if you had created the job after subscribing.
When adding a job to your plan, the job will behave just the same way as other subscription jobs; this means you can refresh its publication date up to 4 months, and also, you will have to keep an active subscription to keep the job published.
Keep in mind that if your job quota is full and you add a new job to your plan, you won't be able to activate your new job until you unpublish any of the currently published jobs.