I recently converted my mod from diplomacy to rebellion and it took quite a few hours. The best advice I can give is to methodically compare the types of files. Open up a rebellion ship entity file and an entrenchment ship entity file and see how they differ, then add the extra lines into the entrenchment file. Then do the same for the research, planet, star, research entity files and so on. Then don't get me started on the galaxy files.
Use the debug log to help iron out any errors.
Here's the link to my post on converting diplomacy files to rebellion https://forums.sinsofasolarempire.com/427240
