If you have a lot of extensions, then you can export your extensions to a CSV file and import the extensions to the new system. It is kind of tedious, but better than making each extension individually. The basic steps go like this:
1) Go to bulk handler on old system, export extensions to CSV.
2) On new system, create a dummy extension or two and then export those to CSV to use as a template. (I say create an extension so that the new CSV has populated data, it helped me know which column of data from the old system to copy into which column of data in the new system).
3) Copy, column by column, the data from the old system CSV to the template. Delete, if you want, the rows for the dummy extensions.
4) Import
Do the same for DIDs if you want.