Página 20 nos estados do corebook
Once you’ve selected a focus for a particular recursion, it doesn’t change
Pelo contrário, como mostra Caleb, uma barra lateral na página 55 oferece
Each time you return to a recursion, your GM might offer you the choice of picking a focus that’s different from one you had last time you visited.
Quanto a focos arrastáveis, a página 52 declara
Some foci are draggable. This means that if you start with a focus in its proper context, you can keep it when you translate to another world. You’re “dragging” your focus with you. If you have a draggable focus but decide to change your focus when you translate, you cannot regain the draggable focus again unless you return to the original world to which it is tied. From there, you can drag it again if you wish.
O que não é a favor ou contra a reatribuição de um foco.
Então, esses são o RAW e a sugestão para o houseruling. Além da contabilidade, não vejo problema em fazê-lo.