Question about kessig wolf run
My opponent has 5 life left
In my combat phase I declared my attackers
Primeval titan, Hunt master of the fells and 2/2 wolf creature token
my opponent declares his/her blockers
Suntitan blocks Primeval titan
Phantasmal bear blocks huntmaster
he/she has one creature left (lets say 5/5 creature) and decided that he/she will take the damage instead of my 2/2 wolf token creature
(note: He/she has 3 life left)
in response I tell him/her that I will pump the wolf with my kessig wolf run for 3 so that I can win the game
Question 1 : Can my opponent suddenly assign another blocker(the 5/5 creature that I mentioned awhile ago) or otherwise change his decision after he/she declared the blockers?
Question 2 : Can I activate kessig wolf run as if it was an instant?