You just need to take it to a luthier to have it switched.
1. It needs to have the nut replaced with a LH nut.
2. The saddle slot in the bridge will need to be filled in, then a new slot routed, and a new LH saddle installed.
It will not ruin the guitar.
If you are buying it new from a dealer, I would ask the dealer to have it converted to a LH model.
Although you'll likely have to pay for the conversion work.
If he won't, I'd find a different dealer.
Actually, if you are buying it sight unseen from a dealer, then have him order it left handed from Guild.
If you are buying it used, then you are on your own to have the work done.