I wrote these notes concerning weapon locks and how to abuse them a LONG time ago. One of my first ROM hacking "discoveries," if one would call it that.
In most FE games the main characters each have their own personal weapons, given the rank "PRF." These personal weapons are given that special property by things called "weapon locks." Weapon locks can be applied to any character with a simple edit using Nightmare's Character Editor, the weapon locks being listed under Abilities 3 & 4.
FE7 has seven total weapon locks (Rapier/Durandal, Mani Katti/Sol Katti, Wolf Beil/Armads, Forblaze, Wo Dao, Dragonstone, and one unused lock).
FE8 also has seven weapon locks (Rapier/Sieglind, Reginleif/Siegmund, Mani Katti (unused), Shamshir, Monster Weapons, and another unused weapon lock).
FE6, however, has only three weapon locks (Rapier/Sword of Seals, Dragonstones, and Wo Dao).
However, should you want more locked weapons than seven (or three for you FE6 users) for your hack there is a way to manipulate these locks. The typical locked weapon has no weapon level, anyone with the ability "Use Rapier/Durandal" can use both swords, even without a sword rank. One way to abuse the weapon locks is to assign weapon levels to the locked weapons. If you were to have, say, a locked sword for a Myrmidon character and a locked axe for a Fighter character; if they share a weapon lock and have weapon levels, the Myrmidon cannot use the axe and the Fighter cannot use the sword because they lack the weapon level to do so. Using this trick one can have a far larger amount of personal weapons than the games would originally allow. This trick works with all of the GBA Fire Emblem games. However, be wary that two characters classes don't gain the ability to use a locked weapon upon promotion. Weapon Lock Abuse requires careful organizational skills.
A small note, any weapon locked with the Dragonstone/Monster weapon lock won't display Might, Hit, Weight, and Crit. It seems to be hardcoded to work this way. This limits you to six weapon locks unless you want this effect.