Upfront: I DMed a lot from 1990 to 2005, but not D&D. So I'm decent quality and experienced, but rusty and a total novice with the 5e rules. I do believe that fun trumps rules, and that alignment describes actions rather than defines them. I also hold that Evil can be extremely selfish, not always vicious & cruel.
Lost Mine of Phandelver: Redbrand Hideout. The PCs find Bugbears playing kickball with Droop, the pathetic runt Goblin, who screeches, soils himself and passes out when the party busts in to kill.
The Bard is a pro (15-year) RPer and is written as naive & optimistic. He defends the unconscious Goblin as a victim. I made Droop exceedingly weak and pathetic (by Goblin standards) thinking that they'd send him into the wild to die. Nope, healed him up and bought him a human child's church clothes, with the intent of converting his alignment.
I found some precedent (besides Drizzt), there's some Orc hero that rejected his heritage, the DMG (p.287) refers to "However, some aasimar fall into evil, rejecting their heritage." To top it off, I realized this morning that the Bard had put in his back story that his Circus was run by a civilized Goblin (can't believe I missed that).
So I'm planning on pushing some epic role-playing to have the Bard work with his former Ringleader to bring Droop over to the light; well, the dimness - Neutral for starters.
Is there a RAW or RAI that prohibits this?
Anyone who also throws in some ideas on how to pull this off with minimum cheese will roll their next Natural 20 because of the Karma from their generosity. So, you know, there's that.