IMO, this is one of those "what's the problem again?" topics. Any art form has to be about experimentation, or else why are there multiple versions of so many songs, perhaps varying in major/minor, tempo, even ending--e.g. "Gypsy Davey" has two different endings as far as story line, and "Golden Vanity" three. If I really like a song--which is totally personal taste, I want to hone it until I've got every quark of the lyric the way I think it "should be." That means I might change it a lot during the "germination" phase, and then freeze it, but I can always rethink it. Besides, you're entitled to think that I'm ruining it while I think I'm perfecting it, so: it's all about freedom. I don't think you can vary a song "too much" as long as you have enough music sense to know what it is you are looking for.

Chicken Charlie