I want that the alias of an object is changed when i run a script In-game
Im a Newbie so easy explanation is appreciated :D

It's as simple as 'object.alias = "new alias"'.

Examples;

Egg.alias = "Bomb"
Documents.alias = "Visa"
Money.alias = "Dollars"

Where the first part is the object, the . seperates it and the alias is the attribute you're changing.

It's the same for attributes you yourself add.

Ok thanks. I've forgot to add ""
That was the Problem

double quotes on a Value makes it be a string (text) value (which means that the Attribute must thus be a String Attribute and vice versa: if you have a String Attribute then its value must be a string value):

player.alias = "HK"

game.greeting = "Welcome to my game, I hope you enjoy it!"

room.description = "blah blah blah blah blah blah blah blah"

orc.look = "He' big, green, ugly, and mean." // the 'look' as a String Attribute. The 'look' can be a Script Attribute instead, but that's not relevant for these String Attribute examples

no double quotes on a Value makes it be an Object (make sure that the Object actually exists, of course) value/reference:

(again, the Attribute and its value types, must match up: Object Attribute and Object reference value)

player.right_hand = sword

<object name="player">
</object>

<object name="sword">
</object>

except for 'true' and 'false', as these are reserved for Boolean Attributes:

orc.dead = false
orc.dead = true

do be warned that there's slight syntax differences between:

in-code (direct coding) and/or using the [EXPRESSION] script option in the GUI/Editor
~VS~
using the scripting options, drop down boxes, and text boxes in the GUI/Editor

yes, it's a bit of annoying confusion, as it's hard to keep it separated/understood correctly.