Yes, by changing your location to Mexico, you can easily install the HBO GO app (settings/general/location). You can even change it back when you are done and the app will remain.
My router has Open VPN on it so I added a Mexico profile just to see if I could get it to work.
However, I figured out that I only have HBO NOW credentials, not HBO GO which is what comes with your cable service. I don't have cable, just an HBO NOW account which there is not an app for, so I can't test this. My assumption is that it would work fine. But would be curious for someone who has an HBO GO account to try it out.
As to the legality of this, I'm not sure that it's illegal in a way that would get you in any sort of trouble. You may be violating terms of service, but looking at it from an objective point of view, LG as zero incentive to penalize any of their customers by spoofing their IP so they can install an app that they probably would love to install, but can't because of HBOs agreement with Samsung. Likewise, HBO has zero incentive to penalize a paying customer for using the service they are paying for. If and when HBO's agreement with Samsung ends, I'm sure all you'd have to do is update and the HBO GO app will appear.
