You'll have to pass immigration (i.e. 'leave the country') to go airside, not just security.

I don't know SCL specifically, but at most airports, international arrivals and departures are segregated, so going back out again will require persuading someone to let you out of the departures area so that you can go through immigration again to re-enter the country for the second time in a day. I suspect they will be very interested in why you are doing this.