I don't have those chops either. Also NAL. The wiki page says Tampering charges require there to be an ongoing investigation, which wasn't the case here, so I'm thinking it wouldn't apply. But! I wonder about spoliation. Spoliation before a case is brought, while not illegal per se, can result in negative inference,
spoliation inference is a negative evidentiary inference that a trier of fact can draw from a party's destruction of evidence that is relevant to an ongoing or reasonably foreseeable civil or criminal proceeding
Negative inference, to my NAL understanding, means the tampered evidence may be taken in the worst light for the defense. Here, it's all resting on flimsy and politically motivated pretext with no evidence. Still.
Needs an immigration lawyer to give an answer to this, but I'm thinking it may be legally safer to have strong encryption and refuse to unlock, rather than to wipe. Not unlocking isn't tampering, so no spoliation, but wiping might be. Well, safest of all is to use a burner. But next best, strong encryption + don't unlock. CBP can confescate the device, but they cannot compel you to produce a pw or unlock code.