Agree, whole-heartedly. I'm willing to make little changes to the specifics of the game but only if it will (a) tell a great story, (b) not keep others from having fun, and (c) not create a ton of extra work for me. I guess preserving the rules are a distant (d). (Except for spellcasting. I enforce spellcasting rules with an iron fist. But anyway...)
The player I keep talking about has decided that her druid eschews metal of all kinds. She decided that her druid cannot attune to anything made of metal, won't wield a metal weapon, won't even wear metal jewelry or carry metal coins. "My druid thinks that all metal is disgusting and she won't touch it...to her, it feels like touching a rotten fish."
Now this is important: she decided all of this on her own, as part of her character's backstory. It was not a restriction that I imposed on her, it wasn't even my idea. She wasn't fishing for any special powers or benefits in exchange for the restriction, she just thought it sounded awesome and wondered if it would be okay. She didn't want to disrupt the whole game, she just wanted her character to have a unique style.
So I said "Of course it's okay," and dove in. She could use pearls, abalone, etc., for currency. She could carry a shark-tooth longsword. She could wear armor made from beetle shell. And so forth. I didn't need to change the rules for what druids can and cannot do, I didn't need to change any stats. All I had to do was create a brand-new coastal village in the game world where they trade this gear (and use this currency), and that became her hometown. No big deal.