Question: If, under your rules, someone purchases Riastrad at a lower Legend, could they purchase it then again later on to override the current Riastrad to add boons and knacks to it as they grow? Or if they want to do that, must they wait until they are higher Legend to purchase it or can they add boons and knacks to it as they progress if in fact they want it that way?
I tried a scientific experiment for you on this one. I waited until John was going over the plot stuff for Sunday's god-level game, and then casually asked, "Hey, if I want to change what's on Eztli's Riastrad, could I buy the boon again to put a new set of powers on it?"
He said, "No, go to hell," and then got another energy drink and went back to Fatebond sheets.
So there's that. That's generally the answer to any "Can I buy X twice" question, since if he wanted it bought twice he'd already have put it in the power's text. But let me go into it in a little more detail and explain why that is and what you can still do to keep your Riastrad relevant and powerful as you go up in Legend.
The main reason we don't allow re-buying Riastrad is that it's intended to be a boon that grows with you - not just new powers you get later, but also the early powers that build the foundation of your warrior identity. Riastrad isn't just a convenient way to use a lot of powers at once and destroy your enemies, but also the battle-fugue that is individual and unique to you as a warrior; it's horrible, but it's also something that is specific and tailored to you, very seldom the same as anyone else's. What happens to you during Riastrad is part of your Legend, which means it is immortalized along with you. We know exactly what Cu Chulainn does in his Riastrad, to the point where we can probably pinpoint almost exactly what powers he used in it, because it's described as part of his Legend in the stories about his exploits. We want it to function that way for Scions in our games, too!
But that doesn't mean your Riastrad can't grow with you; in fact, it will grow exactly as much or little as you want it to. Riastrad activates powers equal to your total number of War boons; when you buy it, that means at least four powers, probably closer to six or seven. But the great thing about Riastrad is that you can add to it as you go along, at almost the same pace as you get new powers, because every time you buy a new War boon, your total goes up and Riastrad needs one new power added to it. You're not stuck with only whatever you assign when you first buy it; if you want new powers, all you have to do is buy another War boon and bam, you add a new skill to your Riastrad bonanza.
So let's use Eztli as an example, because she's our most dangerous and obvious berserker danger to the world. When she bought Riastrad, she had only four War boons total; she loaded it up with Warrior Ideal, Animal Aspect, Do Not Want and Armor Crusher, making her a terrible juggernaut of damage for as long as the boon's effects last. When she next got Mortal Stroke, she added Mother's Touch to the lineup; when she then got Blessing of Insight, she added Lightning Flyer, and so on and so forth until today's Riastrad mess (which is probably wrong on her character sheet thanks to her getting new War boons lately unless we've finally gotten the stupid outlet situation in our house fixed so I can get my computer loaded up and edit it before this goes to press).
So never fear! Your Riastrad does grow with you, provided you continue to invest in the warlike powers it embodies. You'll gain new capabilities and perform new horrors as you get higher in Legend and gain more powers, and those legendary qualities that people have always heard about on your Riastrad will still remain intact and active as you go.