Based on your HP and/or Magicka, these effect has two features:

They both opposite to each other, depending on your percentage of hp/mp.

Example:
Strength of effect | 4>3>2>1>0>1>2>3>4|
Each effect works opposite to each other, like defensive and offensive, CQC (close quarter combat) and Ranged, magic and weaponry.

These effects only boosts the listed skills, so you should think of them as a boosting "Aura".

Say for example, your character is a Thief. You would use " X boost >< Y boost" as X and Y you can choose to customize.

If you choose X as Recovery/Defensive boost, and Y as Sneak/Speed boost, and choose to use it on hp, mp, or fatigue. The results will differ according to the situation:

- You have 100%hp, so your sneak/speed skills will increase their usefulness by 50%+
Then
- You are in a battle and loss 60% of your hp, your aura will change to defensive and HP, recovery spells, will help you recover in battle, although you lost the sneak/speed bonus because you don't have over 50% of your hp.

Mean you this affecting the player character?

Anything like this would be a fairly complicated effect, and would probably work with only one weapon. Additionally, bonuses would probably be lower, and shorter in duration. Meaning that you would only get the bonus to defense and restoration for a few moments after you hit 50%.

Well its would kind of work like a scale in real life, and im guessing it wouldn't work well using hp/mp as a scale. But fatigue can do.

So Fatigue can be a scale for -/+ effects (-/+ as in charges, not including negatives).
Im guessing the effects should work in small increments, but maybe a part of character's stats and not weapons and armor, seeing how equiping multiple of this may abuse it.

Its kind of like doomstone's choosing one class skill effect over learning many skills at once.

An alternative is to attach these stats appropriately to each Vanilla Oblivion Classes, and specifically for custom classes.

I could see spells/powers that work on a conditional basis. Example: if you're a Battlemage and casting spells, the aura would give an offensive boost to your strongest magic skills; once you pull out a weapon though, the aura would shift to defensive and boost your AR/resistances.

Not sure if this would cover what you want. Just a thought.