How would we migrate Alfresco from EE version 4.2 to CE version x? Would we need a project to write scripts for a migration?
I never came across to such use case where customer wants to migrate from EE to CE, but my gut feeling says you should be easily be able to migrate/upgrade using upgrade path which is shown in this link Alfresco Content Services upgrade paths | Alfresco Documentation
Here are my suggestion before you start for migration/upgradation
For rest of the stuff you can refer this blog for upgradation 5 points on Alfresco Upgradation - EnProwess BLOG – Portal | Liferay | ECM | Alfresco | Mobile
EnProwess : Portal | Liferay | ECM | Alfresco | Mobile
...and make shure that your Database is supported by CE - if not, you would also have to migrate your db to a supported product.
Retrieving data ...