You can absolutely use PC-Doctor Toolbox to replace your existing installation of Lenovo ThinkVantage Toolbox. Also, whenever the time comes to by a replacement for your current Lenovo, the software can be installed on the new computer and will continue to monitor for any hardware failures that may occur.
However, I would like to caution you that the only support that is included with the purchase of Toolbox is for the software itself. If you do have a non-software related question you are welcome to post it to the forums, and someone from the community will respond to the best of our ability with our personal thoughts on the matter.
I hope that this addresses your immediate concerns, but if need clarification or have any other questions please let me know.
Thanks,
Kris