Can the unit hold your levy packet if you are put on a temporary profile?

Your unit is not holding his levy. The levy packet requires the medical provider certify that the SM is medically available. If they are not, then the 5118 will not be signed. If the SM is not medically available to move, the provider will not certify that they are.

Only a p3 or higher can stop a PCS

Well, it depends on the severity of what put him on profile. I understand there is some cultural differences but in the Corps you can’t get/execute orders if you aren’t on full duty. If there is an issue/injury/illness or some other factor that could negatively impact assignment there could be a delay to ensure checks and balances are in place and everything is kosher.

It’s not a binary issue because like I said, it depends on the situation. But it’s possible.