I think if you added another dog this would likely become permanent. Also be aware that they can start to guard other things too - like people (for attention), the bed, the best spot on the couch, etc. Sometimes they can be a little unpredictable.Of course these times I also have always removed toys and fed them separately to avoid any potential problems.
You MIGHT have it a bit easier if you got a puppy rather than another adult since dogs are more tolerant of puppies. It's not a guarantee though.
I have one dog who guards food (anything edible) and new toys. The other guards food, people (sometimes), the couch (sometimes). Sometimes a fight will still break out with no resources around and I can't figure out what set them off. It's stressful and difficult and I personally wouldn't want to do it again, even though I have my dogs mostly figured out now and fights are uncommon these days.
I know adding a new dog is fun and exciting, but do try to think realistically about your situation. You know your dog best. Maybe you could try a new dog for a few days before committing to see how it is?