I'll add my welcome to Trainz, and to the forums. As to the problems with the upgrade which many are lamenting today, I'll quote Abraham Lincoln, from his speech to the Wisconsin State Agriculture Association in 1859, "And this, too, shall pass away".
But I don't see that anyone has answered the original question, which was
... <snippage> ... Is there a way to convert the mesh from P[rogressive] mesh to LOD mesh? Any feedback is greatly welcomed. Thank you.
I would say the answer is probably "yes, the content can probably be updated". I would note though, that there is no "LOD mesh". LOD is an acronym for the process by which there are several indexed meshes (~.IM), which the game engine uses to render the image on the screen according to how much of the screen the item takes. There is a tool by PEV, downloadable from Shane's site which will convert a PM to and IM mesh. Beyong that, how easy it will be to do the conversion, and how long it will take you to do it are different questions, which I do not have the answer to. A third different question may be, "is the task worth the effort". When I think about older content, such as you are referencing, I am increasingly coming to the position that the answer may well be "probably not". The reason is that when the old content is updated, it is still, well, old content. Probably for not much more effort that would be spent to update old content, which the community may or may not feel could be release for general use by others than yourself, depending upon the interpretation of the wishes of the original creator as expressed in permissions, one could create new content, to the higher current standards (remember that the older content was made for machines which were slower, had less memory, and processing power). It would take you time to learn to do this, or you might find someone willing to do it for you, but it could be done.
ns
Thank you for welcoming me to Trainz