That code line you posted does not explain very much about the structure of your code and the idea of your approach.
Thus I'll just propose an approach to solve your problem:
1. Use a variable or skill value to determine which camera view mode is activ:
Code:
var camera_ViewMode = 0; // 0=1st Person, 1=3rd Person



2. Define a basic function to toggle between the values. Because in this example we use only two (0 and 1) its rather easy:
Code:
function camera_ToggleViewMode()
{
  camera_ViewMode = !camera_ViewMode;
}


The ! operator negates the value of the camera_ViewMode variable.
Thus !0 = 1, !1 = 0

3. Assign that toggle function to your key. To do so write in the main function:
Code:
on_t = camera_ToggleViewMode;



4. Use the camera_ViewMode variable in a camera function to calculate the desired position of the camera and its angle.
Note: Do NOT use while loops in the camera_Update function in this approach!
Code:
function camera_Update()
{
  if(camera_ViewMode == 0) // 1st Person
  {
    ...
  }
  else // 3rd Person
  {
    ...
  }
}



5. Call this function at the end of your player's while loop (just before the wait(1):
Code:
action player_act
{
  player = me;
  ...
  while(1)
  {
    // movement + gravity + everything else

    camera_Update();
    wait(1);
  }
}



Hope this helps.

About your other question:
You would have to change the camera pan/tilt value with the mouse_force.x/y and then calculate the camera position using thoses angles, the player position and the offset of the camera. (this is the basic idea)