Hearthpwn

what do you think about dropping something and adding a disciple ?

There is one inside. If you add another one, its not HL anymore ;) 

So I read many times that running the Galakrond package is not worth it in HL Priest (except for the hero card, of course), what do you think about it and how has it performed?

I would say that this is correct to a certain extend.

I played Galakrond many times without buffing him to 2nd level. The main purpose of the card is to turn on your value generator hero-power. Single big threat removes come in handy of course sometimes. 

Taking a look at my deck you will see that there are only 3 Gala-activators included. So unless you discover one from your opponent, you will not evolve Gala to his final level. 

But: I still run those three cards, because they are value generators themselves as long as your hero is not Galakrond. Its RNG, but often you get rewarded. 

I consider Disciple of Galakrond good against agro and often i get a 2 or 3  drop from him, so its good for tempo. 
Time Rip is already good by itself plus on top the value form the extra minion in your hand. 

Shield of Galakrond might be the card that can be swapped. Now that we speak about it ...

You could swap it for Bone Wraith, Convincing Infiltrator or even Ruststeed Raider. 

Khartut Defender is always an option, but with 6 Mana I think its too expensive in many matchups.