If you install an upgrade that includes a new hildon-desktop package (as PR1.2 will), it will overwrite the binary installed by my package, and you won't be able to use all enhancements, including more than 4 desktops.

Then you will be able to reinstall modified-hildon-desktop which will restore all enhancements, but might miss new features and bug fixes in the new hildon-desktop. Or you can wait until I adapt the modified-hildon-desktop patch to the new version of hildon-desktop. Depending on how much time in advance I will know which version of hildon-desktop is in PR1.2, that wait might be as short as no wait at all.

You can't use more than 4 desktops in standard hildon-desktop, since there is hard limit of 4 desktops in the program. You can use less than 4 if you want.