it's possible in your studio you have to create a context variable with the prompt option checked like this :

Then you have to configure your FTP component (for example I used the tFTPConnection) and in the "Password" field you have to put your context variable like this :

And when you execute your job it will prompt a window like this where you can set your new password.

But you will have to set it every time you execute your job and it only works within the studio so if you build your job and execute using the scripts it doesn't work.

Hope this helps