Oh, so you are using my first suggestion, just switching the whole image of Player to another frame?
Then it's even easier - you have your ShootPoint on frame #0 for pistol bullets.
Create the same image point (same name and number, but on the tip of your shotgun) on frame #1.
That's it, when you switch to frame #1, bullets will be firing from the ShootPoint defined on frame #1.
You can do all this using pin behavior, it may be a better solution if your are planning to have lots of different guns, armor, backpacks etc.
I added pinnable guns to your project, have a look:
https://www.dropbox.com/s/awm1622c5okjf ... .capx?dl=0