If Paragon of the Amesha gains flying after blockers have been declared, it won’t cause those blocks to change.

When Paragon of the Amesha’s activated ability resolves, Paragon of the Amesha will gain flying and lifelink in addition to its other abilities. However, becoming an Angel will make it lose all other creature types. It will no longer be a Human or a Knight.

You can activate Paragon of the Amesha’s ability more than once during a turn. The second time it resolves, it will get another +3/+3 and gain another instance of lifelink. However, multiple instances of lifelink on the same creature are redundant so you won’t gain extra life from the new one.