My perspective on this would be:
There is most likely a deeper root to re-occuring thoughts.
In this regard it would consider it almost fruitless to exchange negative thoughts by positive thoughts without adressing that root.
I'll give an example:
Lets say you have been treated horribly by humans in your past.
That experience in this example would not habe been "processed" by your past self, most probably because it was impossible at that time.
So you supress the emotions, the horror, the very incident and completely forget about it. It simply doesnt exist anymore in your current awareness.
You would then develop the belief that humans are cold, cruel and so on by there very nature.
This would be an absolute truth for you, because that part that holds it true in a way is STILL in this experience.
You can convince yourself, your current self, that this is not the truth. But you cannot convince your "old self" ( or better your younger self), simply because it doesnt exist for you anymore.
This would be like telling someone who is being tortured "humans are not cruel" and completely ignoring that they are being tortured.
Now as an adult you will most likely interpret all things in this light. Everything will "prove" your belief.
Lets say this issue is very active at the moment in you, waiting to be healed, you will attract experiences that will trigger this old issue.
In the dissociation process you supressed the emotions and installed defensive mechanisms. One of them would be the so-called "ego". It prevents you from re-experiencing this horror by seperating from yourself and your emotions.
One of the most effective means of seperation is "thinking".
By engaging heavily in thoughts you seperate from your emotions and enter a more abstract world.
(You can try to observe in yourself if this is true).
But still, the thoughts originate from somewhere inside of you.
So they dont arise "out of thin air".
You could try to focus on the emotion that is present "behind" the thought or the re-occuring thoughts.
In some cases this might be easy to feel, in other cases it might take extended periods of focus to discover an emotion.
Once you can feel it, you can try to stay as present as possible with it. Without engaging too much in thought.
The more you are able to stay present with (unpleasant) emostions (since they are harder to bear than the nice ones), the more the compulsive thinking will subside and it will reveal more and more of the core issue.
The unpleasant emotions that are triggered in us by outer catalyst are (in my experience) echoes of very old and severe experiences. The are much much "weaker" or unpleasant than the "original" emotion. Nevertheless they are opportunities to heal, to accept and you will reduce the emotional charge each time you are being present with it.
Once you have "dis-charged" the original emotion, there will be no more need and compulsion for that reoccurring thought.
Usually the whole "thought mess" stops long before you discovered the root of it, i found that the willingness to really feel ones emotions and bringing awareness to them is all it takes to stop the compulsive thinking.
A further note on the "exchanging negative thoughts by positive ones and/ or changing one's believes":
I found that you have to be in the position to change this.
In the above example this would mean, once you face that horror, once you experience this (or rather re-experience that state) are you in the position to change that belief and not a second earlier.
Simply because otherwise there will always be a part in you which has a different "truth".
I also found however, once there is an awareness, that the current emotions and thoughts are maybe NOT the truth but stem from an old experience, one is usually at least capable of stopping to feed this (in this case) belief even more with negative energy and thus making it no bigger than it already is.
(I refer to anagogy's post here, in different words)
@plenum that "agua" you mentioned must feel very honored by being referenced by you
@Billy
hmm, my experience is that intellectual analysis will usually distract you from the core issue, since usually the outer appeareance rarely indicates a connection. There would usually be one aspect in common, but it would most probably be overlooked and one would be lost in intellectual abstractions.
Focussing (consciously, not getting lost in it) on the emotion will most probably bring better results, since the emotion will be the same basically, just not as strong.
However, asking for the "truth" to be revealed and confessing the willingness to deal with it ( if that is what you meant), proved to be a mighty tool for me.
I guess this is because it acknowledges that one does not see the true meaning at the moment, honors the fact that one has blocked the deeper truth for unknown reasons and reduces the need for the control mechanism by confessing that one now is willing to deal with whatever arises.
This is a powerful intention which will be noticed by your subconscious control and your guidance.
Apart from that i found deep and maybe sped-up breathing will always help to bring emotions into awareness.
Any type of breathwork would be my favourite recommendation!