for the item world codes, they only appear to be working when you enter the item from the castle. if you decide the level to be 99, it will be stuck at 99. if you repeat the 100th floor 100 times, you'll have a item with 100+start slots and some ridiculous high stats.
wait...what? i got lost after "repeating 100th floor 100 times". what do you mean 100+start slots? do you mean if i set the item level to 99 i can repeat the 100 floors over and over?
and if i set the floor to 100, does that allow me to get hyperdrive faster or no?
that has a lot of options
first, the less abusing method. you only use the Item world floor code and set it to 63 ( 99 ). ( the item world npc will still say "level 1 floor" or something, but in fact you will enter level 100.
( and no, this does not count towards the hyperdrive. for the hyperdrive you need to clear 100 floors and defeat a item god 2 without gency out. if you want to do that, i suggest the unlimited move code and just turn it off once you have it )
now, every time you beat level 100, the item gets 1 level ( item level is bound to cleared floors, not the number of floor you clear ) and 1 additional slot for a specialist. ( also, the stat growth is MUCH higher if you defeat a item god 2 then the growth you get with a normal floor. the +1 specialist slot is due to defeating a item god 2 )
you can now repeat this 100 times ( means, a legendary item is now level 100 and has gained 100 extra slots for specialists ) making the item basically insane powerful.
you can ALSO enter floor 100 of items that have not 100 floors at all, like, take a comon cosmic blade, use the floor 100 cheat, and be on level 100 of the cosmic blade, with a item god ( 2?) holding a yoshitsuna.
for the level cheat, I need to test a few things more, but the process above grants you access to weapons far beyond anything someone ever has created regulary. ( 100 item god 2 on a super robo suit would probably give the item stats in the hundreds of thousands )