Reversing invincible objects to normal objects again?

Com783 writes: Hello there,Q78. How do I make 0-HP units? (Also: How do I make invincible units?)

To make units whose HP reads zero, but are still alive (Note: These units become invincible, as well) use either one of these triggers:

Trigger0 - Display As Objective: Yes / No
Starting State: On / Off
Trigger Looping: No
---------------------------------------
Condition0:
Effect0: Change Object HP - (-*)
Effect1: Damage Object - (-1)
Effect 2: Change Object HP - (*)
* = the unit's maximum HPFrom Scenario Design FAQ

Any idea how to reverse this with a Trigger or something else? I want to make invincible objects for once and after a certain condition is given it gets removed (the object gets HP again).

Greetings,
Com783