Am I right that many schwas become other sounds in songs cause the vowels become 'half-stressed' (I hope you understand what I mean.)? For example, the vowel E in the song 'Silent night' which is schwa in speech becomes [e] when it's sung. Is that right?
Stressed schwa is not permitted in American English, so when an American English speaker has to say a stressed version of what would normally be an unstressed schwa, he has to do something special. Most commonly, schwa is shifted to carat, [ʌ], an open mid back unrounded vowel, the vowel of "putt", "but", "mud", and so on. However, for a literate speaker, substituting a vowel quality suggested by the spelling of the word is possible, like the [ɛ] in the second syllable of "silent" in your example. Even schwa is a possibility, though it isn't totally within the English system.