All right, so I have a bunch of things to report. :-) First off, for the max erosion immunity codes, changing the last two digits ("63") in each code to "FF" (hex for "255"), works! :-) It won't say "99" on the status and force metal screens for each character, but you can equip force metal until you are way above 99, and it won't cause any "alert" or "danger", and the number won't go red, so you do in fact have 255 in erosion immunity. :-)
Next, I discovered that the three codes for "all items", "all weapons", and "all sub weapons" have each code line listed in the opposite order of what is correct, so to make them work it should be:
Have Max/Infinite All Items
00000000 8259e9c8
00000001 011f0002
00000000 8059e9ca
00000009 001f0004
Have Max/Infinite All Weapons
00000000 8259ebd8
00000019 012a0002
00000000 8059ebda
00000009 002a0004
00000000 8259ec84
0000004a 01120002
00000000 8059ec86
00000009 00120004
00000000 8259eccc
00000064 010d0002
00000000 8059ecce
00000009 000d0004
00000000 8259ed00
0000007d 01150002
00000000 8059ed02
00000009 00150004
00000000 8259ed54
00000096 010b0002
00000000 8059ed56
00000009 000b0004
00000000 8259ed80
000000af 010e0002
00000000 8059ed82
00000009 000e0004
Have Max/Infinite All Sub Weapons
00000000 8259edb8
00000001 012b0002
00000000 8059edba
00000009 002b0004
00000000 8259ee64
00000031 01050002
00000000 8059ee66
00000009 00050004
They should work like this. I tested them. Sorry for them being wrong in my earlier post, but that's how I found them.
Third, the "Have All Unrefinable Force Metals" code doesn't seem to work. Through changing all the zeros in the second part of each line of code to random numbers, and firing up the game, I found out that it does in fact affect the force metals and nothing else, so the first part of each line of code seems to be correct, but the problem is that we need the correct value for the second part of each line of code. I tried changing all of those to "00000009", but it didn't work. Just as with the random numbers I tried, it all just messed up the force metal menu and force metal section of the item menu in crazy ways, but without crashing the game. I don't suppose there are anyone in here who is good with code and are willing to try and figure out what the correct values for this code should be? :-P Starting the game with 9 Supra-Force Metal Alphas would be cool. :-P
Finally, something that I think a lot of people playing this game will find of interest: I've been messing around with all those character codes from bowsersenemy to try and figure out how they actually work, and I have succeeded! :-) I have not found any use for that "character modifier" code. All it did for me when I used it was make all the party members disappear from the menu, and when you try to view their status or whatever, the game crashes. However, the the rest are great. The "total party members" code mostly works pretty much just like it says in the explanation. If you change that last "BE" part on the second line to "01", or "02" etc (up to a maximum of 7), it will make it so you have that many party members in your party. As for the 7 "character [X]" codes, they allow you to change the character in that slot to a character of your choosing. So if you input and activate the "character 1" code, and change the last digit from "0" to "1", the first member in your party will be Zero. Leave it at "0", and it will be X. Change it to "2", and it will be Spider. It goes up to "6", and the numbers go in the order of how you first unlock the characters, so "3" is Massimo", "4" is Marino, "5" is Cinnamon, and finally "6" is Axl. This all sounds great, right? Well, it is, but there is a catch:
If you use the "total party member" code at the start of the game, in Lagrano Ruins, when you're only playing as X, you'll just end up with a party of 7 (admittedly all working) X's. :-P And if you use any of the 7 character codes to change any of the characters to anyone else than X at this point, that character slot will just turn into a level 0 X with zero health and no force metal slots, while only the name is changed to that of the character you tried to change that slot into. :-P I haven't tried, but I assume trying to engage in a battle with these broken non-characters will crash the game. But when I loaded up a game save of mine from after Spider had left the party, and activated the code, it made him pop back up in the party, being on the same level and with the same equipment as he was on/had when he left my party.

The other 6 members were also unchanged. So then I started a new game, rushed through Lagrano Ruins until I got to Central Tower, and rushed to the first save device I could find. I then quit the game, activated the code, fired the game back up, and lo and behold, I now had 5 X's in my party again (all being exact copies of my normal X, with the same level etc). So I then quit the game, and changed the "character 1" code so that the first character would be Zero, and when I now started up the game from that gamesave in chapter 2, Zero was indeed in my party, and working (just as with Spider, he was on the level he was when he left my party, and with the same gear)!

I then tried changing my third member to Spider, which as expected just left me with a level 0 bugged out X named "Spider". :-P So from this I think the conclusion is clear: The codes work, but you still need to have unlocked each character at least once before you can use them. But aside from that, as you can see, you can use them to have Zero in your party the whole game (aside from during Lagrano Ruins, outside of the boss fight), you can use them to make it so you never lose Spider, and you can even mess around and change things so you can play with 3 Xs or 3 Zeros.

When I used the code to get two extra Zeros in my party, in that savegame of mine that I mentioned from when Spider had left the party, they both ended up witth the exact same levels, xp, stats, equipment etc as the Zero already in my party. So I guess the codes just makes copies of them based on the instance of the character that you already have. :-)
That turned into a long wall of text, but anyway, that's what I have. :-) I think I'm gonna call it quits now, unless someone can figure out how to fix that "have all force metals" code. :-P Anyway, I hope at least one person out there finds a use for this topic at some point. :-)