Two Axe Mod Questions

Would someone mind advising me on these two questions?

First, when you apply a modification to a weapon, will it always replace the modification of the same type?
For exmple, If you apply a Cruel Axe Haft which lengthens deep wound duration on foes by 33% to Victo's Battle axe which has the following stats.
* Slashing damage: 6-28 (req. 9 Axe Mastery)
* Damage +15% (while Health is above 50%)
* Armor penetration 20% (Chance: 20%)
* Health +30
Will it ALWAYS replace the Armor penetration 20% (Chance: 20%)?

Second,
Which is the best Haft mod to Victo's Axe:
Barbed
- Lengthens bleeding duration on foes by 33%
Crippling
- Lengthens crippled duration on foes by 33%
Cruel
- Lengthens deep wound duration on foes by 33%
Poisonous
- Lengthens poison duration on foes by 33%
Heavy
- Lengthens weakness duration on foes by 33%
Furious
- Double Adrenaline on hit (Chance: 2-10%)
Sundering
- Armor penetration +20% (Chance: 10-20%)
Vampiric
- Life stealing: 1-3 life per hit (for Swords, Axes, Daggers and Spears)
Zealous
- Energy gain on hit: 1, Energy regeneration: -1

Thanks for any help
Drowbane

a prefix mod will always replace the prefix (ie. sword hilt for hilt, axe haft for haft, bow string for string, etc...) and a suffix mod replaces the suffix (ie. sword pommel for pommel, axe grip for grip, bow grip for grip, etc...).

but most importantly, you CAN'T REPLACE ANY MODS ON GREEN ITEMS.

Thanks for the info!