Deception

It makes sense that Harmonium should create a Feruchemist because Harmonium comes from both Preservation and Ruin. Furthermore, Sanderson has said that you can use God Metals to create a Feruchemist. However, this has some problems. The first problem is that Harmonium probably didn't exist thousands of years ago at the start of Feruchemy. But, since Harmonium can be forced to split into Lerasium and Atium even when Ruin and Preservation are combined, maybe they could have been forced to combine in a similar way when Preservation and Ruin were separate? The second problem is that simply eating Harmonium obviously doesn't work. Someone would have tried that during the extensive experimentation happening with it on Scadrial. You would need to do something a little more complicated. Still, I think it is very possible and maybe the most likely option that Harmonium somehow creates Feruchemists! ,

But I still don't see why Odium and Honor became Retribution. Their vessel didn't care at all about any kind of revenge. He wanted to unify the cosmere and enforce peace in his own twisted way. If he really could chose his name, wouldn't something like Enforcement make more sense?

I think that the sheer amount if concentrated energy in the Highstorm would require a ton of stormlight to replicate, but it could be possible. However, the Highstorm isn't just Stormlight but a focus of Honor's power itself, so if that is needed then no amount of normal Stormlight could cause a form change.