The payload would need to slow down to be captured by the planet just the same. Normally you could try aerobraking and the like, but we are talking about relativistic speeds here.

We'd also have limited knowledge of the system itself. Without more accurate data about its objects and their orbits, it'd be almost impossible to plan out orbit insertions even assuming we come up with a means of slowing a probe from relativistic speeds.

Even if your probe had the computing power to run orbital mechanics calculations, there's no guarantee that it'd be in a position to actually make it work when it got there. Of course, that's ignoring the mass constraints involved.

But that doesn't discount the value of even 'just' flyby missions. The scientific benefit would be, literally, incalculable. And the data could help with followup missions, assuming we develop a drive system that could get there and slow down.

The StarShot probes are going to be about a gram. Not much weight to make a primary probe AND a payload.

slowing down from that kind of velocity is serious business. you're talking about braking from 75000km/s to ~8km/s and not blowing up in a spectacular explosion.