Re: do cheat codes break the game?
There's a mod that was originally by Scarlet and is maintained by LittleMsSam that makes Potion of Immortality actually work stop aging. That's what I use. Before I started using that, I would use MC Command Center to add the No Age and Immortal flags to any Sims I wanted to keep around. (I still do that for pets.) It's under MC Command Center -> Sim Flags -> MC Command Center. You can set them to never age (so they can still die from accidents) or as Immortal (or both).

(Tragically, Potion of Immortality is bugged. Your Sim continues to age but it cancels "elder demise" unless you're not actively playing the household,and then they die. So, in a vanilla game, guzzle Potion of Rejuvenation and/or never play rotationally?)
I know both those lots well. Hmm. They should be fine...