emotions can be used as a tool,

That is exactly what I'm advocating. In my original example, use happy/positive emotions to feel better.

We both used the word tool but I was not trying to advocating using "happy/positive emotions to feel better." I was trying to highlight the fact that emotions are a part of an efective evolutionary strategy and by using those strategy to reverse engineer your emotions you sometimes gain useful data to include in a rational thought process.

I disagree that you can use your emotions any way you like. I have not witnessed or read of such absolute and deep reprogramming of the human mind.

Of course you can't literally do anything you like. Look at the previous sentence in my comment to see my meaning in context. What I meant was that you can use emotions in a way that, on the surface, does not correspond to the emotion's "intent". For instance, you can try to feel happy about things you have so far felt sad about, because you rationally prefer to be happy. Of course you won't always succeed fully, but you can try; it's a legitimate and often useful approach.

I agree with this strategy when the emotion is evolutionary defective or if you would become dominated by your emotion otherwise(prevent you from acting rationally). In all other cases it is better to try and extract some useful data from the emotion+evolutionary strategy.

Since they serve a evolutionary purpose even if you could you should not arbitrarily repurpose them

I disagree. Evolution's purposes are not my own. The only purpose we share in common is my own survival, and even then, for me it's an absolute top-level goal while evolution often trades it away for other things.

I did not make the argument that the evolutionary purposes are your own and therefore emotions serve your purposes. Only that you can extract useful data, for your own purposes, from it because it arose from evolution/natural selection.

One counter point which I think can be considered self evident is that experiencing unhappiness can be a strong motivator to avoiding it again.

Certainly that is the evolutionary reason for, and benefit of, feelings of unhappiness. But humans can behave consciously and rationally to avoid problems. Given this, the amount of negative emotions is vast overkill for the necessary purpose of conditioning, and I wish we could decrease it. It's similar to pain, which has a useful purpose, but there's just way too much of it.

What I take away from this is you are arguing for separating your emotions form you rational thoughts so your rational thoughts are not unduly influenced by your emotions. I was not making points counter to this train of thought. I was trying to highlight a use for emotions that not only were not mentioned in your original post, but that your post seem to make points that ran counter to it.

In the cases that the emotional reaction is "overkill" like people that are severely depressed or suffer from other large emotional overreactions seem to be suffering from evolutionary flawed emotional reaction or an emotional reaction that evolved under different conditions and is no longer helpful(based on out of date data). I think we can both agree that these two categories of emotion are unproductive, so I am curious to know what categories you would add to my list which are orthogonal to the two categories I have provided.

Edit: I had misplaced "(prevent you from acting rationally)"