You can. But most typically it is used to treat flares. In general the side effects of long term prednisone use are outweighed by the benefits. Especially as there are so many other options to manage asthma with far better side effect profiles.
Maybe. Prednisone is one of many possible treatments for asthma. Many asthmatics take an inhaled version for daily maintenance, which decreases total body exposure to steroid side effects by putting the drug at the site of need. When used, it is best under the supervision of a physician.