The Broken Hourglass - Tinkered Spells @ Official Site

The Broken Hourglass site has an update from Planewalker that looks at so-called tinkered spells in the game:

Characters in The Broken Hourglass have an almost unlimited ability to customize their spellbooks through the use of the Tinker Spell interface. A "tinkered" spell is one defined by the player, selecting from a menu of spell sources and effects and given a player-defined mana strength.

Once one of your characters tinkers a spell, every member of the party may use it, if they have the necessary magic skills and mana to cast it. The entire party "learns" the customized spell. Tinkered spells are remembered with your saved games. You may, at your option, later delete a tinkered spell when you feel it has outlived its usefulness.