Every item I've looked at doesn't seem to accept this enchant. Can you only enchant non-magical clothes or robes with it?

Plus: Does the + magicka aspect of it stay at 10%? If so, is this a bug?

bumping

Dont use those double enchated things, find single enchanted items, for example, thalmor robes have a singel enchant of reduce destruction cost, so I used , and enchanted 4 of my items with that, and I have reduced my destruction cost by 90 percent.

You can put it on the armour slot.

The enchant for fortify school/regen is a "special" enchant that uses two effects for the price of one, but the trade-off is that it is not as good as using just one or the other. For example, the magicka regen from the hybrid effect won't ever be as good the regen effect all by itself. Also, only chest armor or robes/clothing take the hybrid effect.

-Loth

Can you bypass that problem with the Extra Effect enchanting perk and get the double effect with normal strenght on both effects ?

That enchant can never be as good as it will be on the Master Robes, sadly.

But you have no armor and have to use skin spells, with the alchemy enchanting loop, it can be, make a fortify enchanting potion, go enchant something for fortify alchemy, go back to make fortify enchanting, and then back to fortify alchemy, and it will progressively get much better.

That particular enchant (all versions of it) can only be put on a chest item, so you can't stack it. I think it tops out at 15% magicka reduction, and 50%? magicka regeneration (not sure about the regen amount).

With the full magicka reduction enchants, they can be maxed to 25%, and can be put on 4 different slots, so with full perks and 100 enchanting, you can actually have two schools that cost 0 magicka to cast any level spell. At that point, magicka regen is unimportant.

To answer another part: enchants can only be applied to items that have NO enchants at all. That includes adding a second enchant if you have the perk- it still has to be done to a "blank", unenchanted item.

At 100 Enchanting it only gives a 10% magic regen I think? So you would have to make a pretty awesome potion. I know it can be done, but I hate leveling alchemy so I've never fooled with it.

Yes. Getting the Extra Effect perk allows you to mimic having the hybrid effect, but the numbers will be much higher.
-Loth

What I find somewhat annoying is that Fortify (Magic School) may be applied to Head, Neck, Chest, Hand (ring), but NOT to Bracers/Gauntlets and yet one can find in game items like the Imperial Bracers of Major Destruction (arm slot). The logic (if any) used in determining what slots may be enchanted with specific enchants escapes me with this kind of discrepancy. Ah well, I will be modding this for consistency sake and personal peace of mind for myself.