I have done that in the past and it work quick and well, both for Lat and other fares. Good thing it is Lat so you can avoid the $150 change fee, you still have any fare difference to deal with. g46r raises a good point about validity being the original issue date.

You can cancel online easily and rebook a completely new and seperate reservation. I have had cases where although a fully refundable fare, the refund wasn't automatic (I've even had an automatic reply stating the fare wasn't not refundable but a credit would be established); I'd either have to call in or email a refund request. It can take from a few days to almost two weeks to get the refund on your cc. Keep your original booking/fare rules, it comes in handy when replying to CS to prove your case.

All in all, do it online, change your original booking if you know you're going to use it up within a year.

But don't be surprised if you have to send a follow-up email for the refund (full or partial depending on what you change the booking to, if any). I've never had to actually fight to get a refund.