Unlimited "Free" listing option

Many Blessings,

Is there any way for me to set a listing duration to “unlimited” while limiting the duration of upgrades to 30 (or any) amount of days?

I want to have a “free” option that lasts for an unlimited amount of time. To do this I set the duration of free listings to 9999 days, but I realized the upgrades would also last for 9999 days, and that just wont do.

I would also like to remove the text that says a listing will be deleted after it expires, because my site is setup to revert payed listings to free upon expiration.