A belt normally squeals because it is worn or loose. A belt dressing spray (which is a bit like an adhesive) will temporarily give it a bit more grip, but will wear off pretty quickly and you will be back to square one.
all you need to do is slacken off the alternator pivot bolts and wind the tensioner in a little bit, if you over-tighten it you wont break the belt but will give the alternator, water pump and aircon pump bearings a hard time because of the extra load.
Modern poly-vee belts are made from polyurethane and use either polyester, glassfibre or steel cords as tension members and are incredibly tough and long lasting. I once went to order a new belt for my Jazz from Honda after 50K and the salesman said the belts do not have a finite life, you only replace them when visible cracks appear, he had never replaced the one on his Integra and it had done about 140K.