Max credits at the start of the game save. Before using this save make sure you get the "complete Prologue A" achievment.

I have only unlocked the credits so no achievments will pop.
It should make the game alot easier if you buy plenty of the abilities, character parts and weapons.

Go to "My Page/Customisation/Character Parts/ and press Y. You have 99999999 credits.
Just keep pressing A to unlock as much as you want.
 

WARNING: There are achievments for the following so do not buy 100% of each category if you dont want to unlock the achievments yet. Also the purchases are random so you never know what you are going to get.

Weapons Master 25 G [SECRET] - Unlock all regular weapons and grenades.
Prove Your Mettle 25 G [SECRET] - Unlock all the Abilities.
Warrior of Many Names 20 G [SECRET] - Unlock 100 Noms de Guerre.
A Collector"s Collector 50 G [SECRET] - Unlock all items (weapons, Abilities, Noms de Guerre).

Kero