We've created and verified the .prp file for our site, and will probably upload it this week.
This is just the 'first phase' of an ongoing installation, and we'll most likely beadding around 20 additional meters every month or so, as new houses are finished. Do we add the new meters to the original .prp file, and then do acomplete upload of the entire network file each time, after we've verified pulseconstants and synchronised readings for the new meters?
Also, as new houses are completed, it may be necessary tochange the network routing, as signal paths may be blocked by new structures. Again, should we do all this in WavenetExplorer,and once we're satisfied everything is correct, then upload the amended full .prpfile to PnPSCADA?

Great!
I don't know if you do any changes to the setup/routing in pnpscada? What I normally do, just to make sure, is to freeze either the one or the other. In other words, while I work on the prp with WavenetExplorer, I don't update pnpscada, and when I work in pnpscada, I don't change stuff in WavenetExplorer.
So, what I would have done, is:

1. Work on the prp exclusively at first
   
2. import prp to pnpscada
   
3. work on pnpscada exclusively
   
4. export prp from pnpscada
   
5. work on that new prp exclusively (while pnpscada setup/routing is frozen)
   
6. import new prp to pnpscada
   
7. work exclusively on pnpscada (while wavenetexplorer is effectively frozen)
   
8. etc.: rinse and repeat.
   

For doing little changes via WavenetExplorer or via pnpscada, where the principle is always to change the MIU itself, e.g. start readings, pulse constants, alarm settings etc. - in other words since the source device has changed - you don't have to do any import/export of the prp.
While the prp file logs the last time you've written or read values, e.g. start readings and pulse constants, pnpscada doesn't import them from the file, but reads them from the device itself. Where possible, we've always followed the principle that pnpscada reads the device itself.
The prp import/export is mostly to create your routings and meters with the correct dependencies on each other.
Of course, the once exception: if changing the pulse constants in the MIU with any outside program, you have to go check that box in Meter Details on pnpscada to tell the system to read the constants again, because pnpscada caches that info, and doesn't read it every time, in order to save battery power.
I hope the above answers your question?

To clarify: the .prp file should reflect everything on the site (on a single WavePort).
So yes: you would import everything (all phases) again every time you complete a new phase. It should not mess with your existing configuration in pnpscada as long as you didn't change the routings. Conversely, if you had to change some existing routings because of new structures, that would change the setup in pnpscada of the routings surrounding the old elements.
If you know your pnpscada is right, before you start a new phase, I strongly advise you to use the export from the waveport to get a .prp file that exactly reflects what is in pnpscada, and then use that prp to do your new phase.
WARNING: If you use your old prp for the new phase, but you've done changes to pnpscada, your changes in pnpscada will be wiped out when you import the prp for the new phase.