Change Perk is a great school of magic for people in Skyrim who want to be better at defence.
Alteration is a must-have skill for any mage in Skyrim, as its defensive spells will shield you from hits that would normally kill you and protect you from magical attacks. Most mages have low health, so spells like Oakflesh from the Alteration school give them extra defence.
That said, the Alteration skill tree has a number of bonuses that can be used to boost and improve the protective powers. These benefits range from lowering the cost of basic magicka to absorbing spells and everything in between.
Stability

Protection spells only last for 60 seconds, but some fights will last longer than that. This can be very bad in the middle of a fight. All of the Alteration perks last 50 percent longer thanks to the Stability perk.
This works great for long battles and saves magicka over time because you won’t have to cast the spell as often. This perk can be used together with Alteration Dual Casting to make magic last 3.3 times longer.
Apprentice Alteration

Apprentice Alteration cuts in half the cost of apprentice-level spells that change things. This makes early-game magic like Stoneflesh much more affordable. Early on, important defence spells cost a lot of magicka, so it’s great to have a way to fit this important spell into your budget.
Unfortunately, the only spells at the apprentice level are Magelight and Stoneflesh, which makes them hard to use.
Novice Alteration

Novice Alteration is available from the start of Drive Mad game and is the gateway to all other Alteration perks. It is the starting place for all other perks. For a pure mage run, it’s important to lower the cost of casting important early-game spells like Oakflesh and make them work with a smaller magicka pool.
It’s less important for spellswords because they usually play with light or heavy armour, so they don’t need protection spells as much.
Adept Alteration

With Adept Alteration, you’re halfway to becoming a master of this defensive skill. It also marks the point where spells start to cost a lot of magicka to cast, even if you have a big magicka pool.
This is a great investment, and it leads to the Expert Alteration and Stability perks, which are both very useful for a high-level mage. It can’t be bought until you have level 50 in Alteration. The perk lowers the cost of powers like Telekinesis and Ironflesh.
Expert Alteration

Getting good at the Alteration skill isn’t as easy as getting good at Destruction or Conjuring. Some of the best magic security comes from expert alteration spells, but they are also some of the most expensive.
Ebonyflesh, Paralyse, and Ash Rune are all great spells with strong effects that cost a lot of magicka to cast. Since Expert Alteration cuts their costs in half, it’s a must-have if you’re playing on a hard setting and need the extra boost.
Master Alteration

As you went from beginner to master, you cast a lot of protection spells that helped you stay alive in battle. Now that you’re a master of the skill, you’ll need a perk to make it easier to cast magic of this level.
Like the other perks, Master Alteration cuts the cost of master-level powers in half. Some of the spells at the master level are like Dragonhide, which lets you avoid 80% of physical damage for 30 seconds. Even with the perk, it’s a pricey one, which makes purchases in magicka cost reduction jewellery much more worth it.
Alteration Dual Casting

With the Alteration Dual Casting perk, spells can be boosted to make them last twice as long and cost twice as much magicka. This saves magicka over time, especially when fighting harder bosses.
You’ll only have to cast protection magic once, and thanks to the perk, they should last through most fights. When you use Dual Casting, the perk doesn’t get stronger like it does with Destruction Dual Casting or Restoration Dual Casting.
Magic Resistance

Magic Resistance gives you a passive buff that stops some of the damage done by spells. The amount of damage blocked depends on the level of the perk. There are three levels of this perk, each of which blocks 10, 20, or 30% of a spell.
Rank 1 needs Alteration level 30, so it’s easy to get early on if you use your skill points well. If you combine this perk with Ironflesh and other spells, your mage can become a tank in a fight.
Mage Armor

With this perk, defence spells work much better than they did before. Mage Armour makes the armour rating that spells like Stoneflesh give you even better. Each of the three ranks increases the score by a factor of two, two and a half, or three.
Even a simple spell like Oakflesh can add 120 points, which is more than Dragonscale Armour would give on its own. This perk is the best way to turn your character into a beast without having to go find high-end mage gear.
Atronach

When you’re not the one casting the magic, mages are a pain. To stop them, you can buy the Atronach perk to take some of the magicka from spells cast at you. At rank 1, you’ll be able to absorb 10% of a spell. At rank 3, you’ll be able to absorb 30% of a spell.
When you learn that dragon screams count as spells for the perk, it gets even better. Also, because this perk is so powerful and gives you a magicka pool that fills up quickly, it needs 100 Alteration.