I have mild lung scarring from gerd. I have never smoked. If we can stop the acid, can my mild lung scarring remain static?

Yes, but . . . Treating your gerd is essential not only to prevent further lung irritation/inflammation/scarring, but also to recude the very real risk of esophageal cancer. See a gastroenterologist for upper GI endoscopy if not already done, and advice about treatment of your reflux esophagitis! esophageal cancer is a big deal, and not always curable (unless caught early, or prevented in the first place)!
Maybe. If in fact your lung scarring is due to gerd, an endoscopic or surgical procedure that controls gerd from an anatomical standpoint should arrest the scarring. The scarring may be due to another cause however, and you might never know unless you eliminate one potential cause.