if you aren't adding new islands duringthe sim, then just store them before the sim and because it's vertices you could even use the index instead of using the islands.

you don't value to worry about propagating the (attribute) ID yourself, because the way it behaves is that—then it captures or store an attribute it propagates / gets inherented by any geometry made from it either extruded, duplicated, or even instanced on it.

(there are some cases though, that will loos attributes when on certain types, or certain domains, and or when using certain operations (nodes), but generally it will propagate on it's own.)

if you aren't adding new islands duringthe sim, then just store them before the sim and because it's vertices you could even use the index instead of using the islands.

you don't value to worry about propagating the (attribute) ID yourself, because the way it behaves is that when you captures or store an attribute it propagates / gets inherented by any geometry made from it either extruded, duplicated, or even instanced on it.

(there are some cases, though, that will loos attributes when on certain types, or certain domains, and or when using certain operations (nodes), but generally it will propagate on it's own.)