From what I understand Preordered games will come with three codes:

Pre-order early access code
Pre-order bonus code
Registration/Product Code

Your preorder early access code and is limited in number and you can only use it before launch...

Your preorder bonus code gets you the items, but you can use it until December 31st. The items are delivered to the account that the preorder bonus is registered to.

According to this information, so long as you have the preorder bonus code, you can choose to put it on any account you want so long as it's a platform/region match. (bonus codes for PS3 and PC are different and don't work cross platform. Same for JP/NA/EU codes. They don't cross regions.)
Your preorder bonus code gets you the items
The registration code allows you to create the service account

If you have a service account already, why not just put your preorder bonus code on your existing account to put those items on your character?