Ah ok, I misunderstood.
That's because the attachable is located in pyro.ini, which is in the same directory as the flame.
If you'd like to change it to something you made, copy the correct part from pyro.ini and paste it in a new file. Then you can modify it at will without ♥♥♥♥ up other things. Also, change the name to something else, otherwise it will conflict.
Find the following piece of code in DropShips.ini
Code:
Flash = Attachable
CopyOf = Jet Flame A
And replace that with your newly named part.
Then all you have to do is make sure that file is read before your dropship.
Unless I did something horribly wrong, this should work.