Derren said:
If the DM allows such cheese. A sensible DM wouldn't.
I disagree. The item creation rules are there for players who wish to create items, regardless of what they're intended to do. Now, there's something pretty sinister about wanting to make a cursed item and forcing an unwilling creature to don it with the intention of "redeeming" it, and I would tend to believe most Good creatures wouldn't try it.
But in changing the alignment of a Dragon, unless it's [Evil] (as opposed to Evil as an alignment), I would rule that it's possible. I mean, we had previous editions for a reason; it's just a shame most of their wisdom wasn't carried over.
Plus, you have to consider the in- and out-of-game reasons for allowing such a feat.
1) What are the motivations of the character?
2) What are the motivations of the PLAYER?
3) Is it cool, and does it add something interesting to the story?
Those would be my criteria. Hell, you could have a whole campaign arc about trying to raise baby Dragons in a world where Green Dragons are evil and slain on sight by just about anyone, on principle. What's the projected survival rate of a Good Green Dragon in a Dragon's world? What are the poor little darlings going to eat? Who's going to teach them all about their innate spell-like abilities? Where are they going to stay? Oh yes, lots of chaos, lots of potential.
I ran a solo campaign where one of the NPCs was a hatchling "Space Dragon", I think they were called (from Spelljammer). My player had a hoot of a time trying to teach her the ways of the world... but it's not for everyone.