I'm struggling with this decision now. I started a legacy and put tons of time into the first generation, following rules, but using travel to extend the lifespan and accomplish more skilling and wealth. The first gen had enough happiness to buy the Teleporter and Moodlet Manager, and since getting those I'm finding it practically impossible to resist using testingcheats for teleporting and mood manipulation, even on gen 2, since it's essentially the same as using the LTRs, only more convenient.
To make matters worse, my gen 2 child got mostly garbage traits (clumsy, heavy sleeper) that kept her from being an interesting sim, so I made up a rule for myself about changing one trait, and you can guess what that led to.
I need to decide where to draw the line before gen 3 gets born, or else I'll be managing toddler moods, changing traits again and again, then give up on my family because I meddled with it, despite truly working up from poverty without cheats.
I'm already thinking of them as my "generational game" rather than "legacy", but it's a slippery slope leading to no more fun.
I'm wondering what kinds of "fudging" other people do in generational games when they decide to deviate from the rules.