Because another site has already done these codes to a much better extent than I possibly could. I'll post the tools you will need, and a link to the site. Later, I'll post the known individual character code.
As the program you need for this is freeware with no claims to ownership, I decided to attach the file to this post. Check at the bottom of this post for a link to the file.
Make sure the game ID is 374 and the region is USA and auto-identifier enabled.
This is the codes. Both PAL (European and Australian), and NTSC (American, Canadian, and Japanese) The codes listed here allow you to have the FE6 Images.Because there are no actual "masters" of these codes here (I suppose I am the closest thing FESS has in terms of a constantly active member, though I'm not by any means the best, if only because I don't even have the game at this time), help with these will be limited to this topic. Post all questions IN THIS topic.
Basic Quick FAQ:
Q: Can we have infinite custom weapons/Infinite Forged weapons?
A: No. Due to how the custom weapons are stored in the data, infinite custom weapons are impossible
Q: Can we visit the shop infinite number of times, then?
A: As of this FAQs Making, no.
Q: Why aren't there codes for more then Ike and Titania on the official Codejunkies site?
A: There are two reasons for this. One is that except for Ike, Titania, and Oscar, the other characters have no permanent place in the data, making modding them somewhat hard. The second one is that Codejunkies is lazy.
Q: Is it possible to get characters like the Black Knight and such on your team?
A: While it doesn't work the same as the GBA games, yes. Explanations can be found within the topic.
Q: Can Sothe Promote with codes?
A: Yes. I believe this is addressed within the website I've pointed out above.
Q: Can I assign skills to anyone I want. For instance: Give Ike luna?
A: Yes, you can. While I believe the example I used is... questionable at best (due to it being an occult skill), the concept is possible.
Q: Hey, I wanna get some of the characters from this game that are in FE10 but Unusable so I can train them up for then! Is that possible?
A: No. The game doesn't transfer EVERYTHING from the previous games. Just the info from set characters.
Q: What should I do to ask questions?
A: Just post them here. If I feel that it is something that should be added to this small little FAQ, I will.
EDIT: Any time it says "In the topic," it is referring to the FESS4 topic, found
here. No, I'm not bothering to directly answer anything found here,and I'll just keep pointing back to this if you ask questions that have been answered.