At Brainshare I discussed upgrading/migrating three NDPS servers (in orginal tree) to one iprint server (in a new tree).
The migration steps from 3 NDPS Servers (in old tree) to 1 iPrint Server (in new tree). These are the steps that we are think about, all looks good except when we get to step 4. There is no iprint.ini file on the old NDPS servers. Any ideas?

1) Setup DNS on each of the NDPS servers using /DNSName = (each server has its own DNS name and ip address)
2) Make sure iPrint support is not enabled on all printers
3) Deploy iPrint client
4) set UpgradeNDPSPrinters entry
5) enable iPrint support
6) Since you are moving across tree boundaries - you are going to have to create the printer objects in the new tree. (make sure that the printer name remains the same!!!!) So the client will find that entry on the new server. The migration tool will not work for this situation (since you are creating a new tree)

6a) You will need to go to each manager (console on the server) and backup the database.
6b) This will generate a .csv file in the sys:\ndps\<psm directory>. (You will just have to edit the .csv files to point to the new container. You can pull it into excel and do the edit on it.)
6c) Then run pagen.exe (using each of the .csv files) from a workstation dosbox (make sure your primary tree is set to the new one)
6d) This should give you the objects and printer agents.

7) Depending on how many drivers you need for your print environment, you will either need to copy/prune the old file system to the new server or just re-add all of the drivers to the new resdir
8) You will then have to re-assign the drivers for each new printer object in the tree
9) Change the DNS entries for the old servers to point to the new one
10) The clients should not know the difference on the backend change.
11) Wait a week then down the old NDPS servers.

The UpgradeNDPSPrinters entry will only work for printers in the same tree, so you will have to create a dns entry for each.
You will also have to merge all brokers into one set of drivers (and then re-assign the drivers to each printer).