You can't put it in any slot. It has to follow the next available slot. So if you have 10 weapons, you will have to put it in the 11th slot. If you put it in, for an example, slot 30, the game will not register it until you fill up slots 1-29.
0x722cb2ef is the ID and 0x108 is a index in a table. ID is the first 4 bytes and index is the last 4 bytes in a weapon entry. For weapons, the entries start at 0x548.
I've uploaded a simple save editor and the source if you want see an example on how to add a weapon. You can add max gil, cp, inventory (excluding weapons, armor, and accessories), and DLC items.
Source
Save Editor