There's no code for a 'flametongue' or 'frost brand' to do a few extra points of damage to selected monsters.
With just a text editor:
*Change the 'long sword vs giants' to 'long sword draconslayer'. Then set all the dragons to be 'True Giants' (and the giants not to be). Ta-daa, instant long sword vs giants!
Zhentrim and Zhentil sprites should be available in one or the other artpack. If not, you can run Gold Box Explorer and capture the icons, then stick them in.
Give the Zhentrim Mages Minor Globe of Invulnerability, Invisibility, and Protection from Normal Missiles as a precast ability.
An all-EGA hack was recently released.
Also, as a nitpick, maximum levels are 40, not 18, for humans. I believe level limits can be changed using FRUA98 or RC_EDIT.