Nope! If you check out the script you'll see a for loop that says:
for(int i=1;i<100;i++) //function here
When you duplicate your lights, the duplicated version will have the next number on the end. Duplicating flash_1 will give you flash_2, duplicating flash_2 gives flash_3, etc.
The for loop applies the function it precedes to all of the lights and billboards in your map, as long as the name stays flash_x, flash_point_x, etc (where x is any integer between 1 and 99)
You can create up to 99 of each type of light. If you make more than 99 windows (for some bizarre reason), just change the 100 to a larger number in the appropriate for loop.
No need to worry about scripting the billboards though, they're connected to the flashing lights, that means that when the connected light flickers, so do the billboards. They're all connected to flash_1 I believe, so don't delete or rename it!