No, and thats the beauty of Dictionary object. You can simply do:
Dictionary: Add key "your_key_name" with value "your_key_value"
any time you want. If key with that name do not exist, new key will be created. If key with that name already exist value will be overwritten.
So you can do stuff like this:
On left mouse click -> Dictionary: Add key "click count" with value Dictionary.Get("click count")+1
On first click it will create a new key "click count" with value 1
on second click it will set key "click count" to 2
on third "click count" will set it to 3 etc.
Think of it as a global variables that can be added/set/removed on runtime any time you want
Oh and key values can be anything. Integers (1, 2, 34, 56..), floats (1.2, 44.34, 4.666...) or strings ("aaa", "bb bb"...)
EDIT: But if you want you can make a text file with all your keys and values already typed in and then use AJAX to load that file into a Dictionary object. This way you starts your game will all necessary data you need for your game!