I've read this interesting heatpipes fundamentals dissertation.

Anyway i have some questions left:
- is it necessary to replace heatpipes after many years of use?
- can they be bended with regular pliers?
- why did you clean them with alcohol before installation?

No, heatpipes are sealed systems and made of corrosion-resistant materials. By the time a enough coolant evaporates from normal operation the machine would be archaic and a cheap replacement cooler would be much easier to install.

Yes, they can. I have tweaked them to allow for tight installations, but great caution must be taken not to crack the pipes.

To remove grease and oil from fingers as well as dust and other debris. Makes better contact with thermal paste and therefore improves cooling efficiency.

I'm not so sure. I'm afraid not all of them. The materials are different.

A blowtorch will make the tougher ones more malleable.