They could probably refuse to acknowledge it’s purpose as a planet annihilator and just say that the rebels launched an attack that destroyed a brand new station and its crew, justifying the use of additional force against the rebels (also they’re the Empire and they don’t really need to care about PR)
it would also be easy to defend anything about the planet destroying capabilities by saying that while it was a powerful weapon it was meant only for worst case scenarios where vicious rebel dissidents had taken over uninhabited planets. or they could probably even say that formerly separatist rebels had created a similar weapon that this was built to counteract and defend from
Fair enough I think they’d either sweep it under the rug or like the other guy said just lie and call it something else tho I would be concerned about the truth coming out one way or another just based on how many Hugh ranking imperials weren’t to keen on what happened to Alderaan as well as all the existing rebels corroborating stories of a planet killer plus the whole missing planet lol