Do you know ... ?

Fernando Carreiro  
XasmY: Do you know if it’s possible to run an external script (i.e. outside MT) which sends a signal to the EA so that the EA executes its action accordingly ?

If yes, how ?

Yes, it is possible for an EA to receive information from outside of MetaTrader, just like it is possible for an EA to send information outside of MetaTrader.

The information can be send and received via, Shared files, Named Pipes, Socket communications, Windows API messages, and probably many other forms of data exchange.

As for how exactly, that depends very much on what kind of information it is, how the EA must react, how the EA already functions, and the abilities of the coder (it is not something that will be easy for a newby coder).