assuming you already have a projectile bp working with spawning.
Your character bp would handle input(fire rocket) and state(power up or not)
fireEvent->spawn projectile->cast to your projectileClass based on weapon equipped->check if character is powered up->call projectile’s setDamage function(public or through interface) to set it’s new damage.
in project tile graph, you need to create/implement a public function called setDamage, which just set the damage of your projectile.
other blueprint don’t need to change because old graph should just work as is.