Interesting Hacking Question

Alright so here is what im thinking can someone please tell me if my thinking is wrong.

So i was playing with super soldiers today and there is a box that gives 300 hp. Why cant someone in theory take the code for the 300 hp box and make it into a button you can press that will automatically give you 300 hp even if you do not have the enduring phoenix in your inventory. In theory you could last forever because every time you get close to dying you would just press the button and give yourself 300 hp. Thoughts on this? Or is what im thinking of impossible to do?