20% enchantment mods

i was wondering how this mod exactly works. say i have a staff with the 20% enchantment mod and i cast an enchant. then i switch to a staff without the 20% enchantment mod. will the enchant then last 20% longer, or do i need to keep it on the weapon with the mod?

you need to keep the staff on for the mod to stay

Wrong. Modifiers only need to be equipped while casting for them to have effect. Unequipping a 20% enchanting staff after casting an enchantment still results in a 20% longer enchantment. Halved recharge time and halved skill recharge also only need to be on while casting.

The same applies to an attribute+1 (20%) mod too. You can use this to cast your spell to get the 1-in-5 chance of the increased attribute, and then switch to a different (e.g. health +30) weapon after it is cast. This is particularly useful for long lasting hexes.

Heck, if you fire a flatbow while under apply poision, and then switch to a poisionous bow while the arrow is in mid air, when the arrow hits it will have a 33% longer poision duration.

Lots of little things like this exist in the game, since certain skills only look for the stats of the item you have equiped at a certain time.