What Stephen+Katt is saying is mostly correct. Pre-existing project plans in Paratext 8.0.100.76 or later will work when upgrading to Paratext 9. However, some of the improvements to Project Plan functionality may not be available. Because they are maintaining two versions of Paratext, currently, it is necessary that new plans be made on computers that have Paratext 9 installed.
Stephen+Katt is also correct that within SIL there is a strong request from management that plans have the same same six stages, with the same names and in the same order. (I believe this is also true for Seed company, and most other Bible translation organizations) Having some uniformity in the plans allows for better data collection and management and reporting to donors. Speaking only for SIL, it is possible to reorder, move to a different stage, add, delete, or rename tasks, just don’t change the stages. The easiest way to do this is start with either the SIL Base Plan or the SIL Compact Base plan and modify it.
There is a lot of good information about project plans and how to work with them on the Paratext website. I will not duplicate all of that information since it is already nicely organized here: Project Plans
If the user in PNG has specific questions not covered on the Paratext website, then please write back and we will try to resolve the problem