1) Replace "Player" sprite with "Drone" sprite:
Give both your character and drone sprites the PIN behaviour
In your coding, whatever trigger causes the switch to occur, add "Unpin" player sprite and "Pin" Drone sprite to the player box sprite. Do the reverse for when you want to switch back
2) For deactivating the player controls and activating drone controls:
In event sheet, put all player controls in a group and all drone controls in a separate group.
On the character switch trigger add "Disable Player group controls" and "Enable Drone group controls" (You'll need to disable drone controls on layout start)
Do the reverse for when you are switching back.
You'll probably need to control these with instance or global variables, something like player control = 1 (for player) and 0 (for drone) and add these conditions to your coding accordingly.
If you want to keep both sprites on screen, ignore step 1.