Yes, you can upgrade the weapons on the Scramjet in GTA Online29. Here's how:
: Select weapons in GTA Online can be upgraded to Mk II with a Weapon Workshop2.
: To upgrade weapons to their Mk II variant, you need to own a Weapon Workshop, which can be obtained through29:
Purchasing the Weapon Workshop for your Avenger9.
Purchasing the Weapon Workshop for your Terrorbyte9.
Installing either the Weapon Workshop bay or Weapon & Vehicle Workshop bay in your Mobile Operations Center9.
Purchasing the Weapon Workshop for your Arena Workshop and hiring the Weapon Expert24.
Setting up The Diamond Casino Heist, which provides a Weapon Workshop in your Arcade’s basement until the Heist is completed or canceled9.
: You can modify the Scramjet in your arena war workshop1. To do this, you need to press right on the d-pad when you get into your Scramjet4. You also need to purchase the extra mechanic in the Arena War Workshop4.
: When you buy the Scramjet, the weapons are already installed1.
: The Scramjet has machine guns in the front and missiles on both sides1. There is a limit of 20 missiles1.
: The Scramjet also has a jump and boost feature37. The boost lasts for 2.5 seconds3.