Can I install Ford 5.4-liter Engine in a Crown Vic?

Can I install Ford 5.4-liter Engine in a Crown Vic?

And yeah what the things that I should modify?

Yes.
Mounts, computer, trans adapter

The 5.4 is a junk motor. They are notorious for valve issues and spark plug threads disintegrating. You're better off going with a DOHC 4.6 motor.

You could, but most the intake manifolds available would be for trucks, which tend to be taller (longer runners encourage low-end torque), so there's would be hood clearance issues. There's probably some aftermarket ones available though

Possible, but why would you?