Can you “downgrade” a Sitefinity 4.x project to a lower edition?
Yes, but please, note that by downgrading to a lower edition you won’t have access to the features included in the higher edition and more importantly, any custom development work based on those features will be lost. For example, if you develop your project with our trial version of Sitefinity 4.x Enterprise Edition and then purchase Sitefinity 4.x Professional Edition, you will lose the custom development work related to the features that are available in the higher edition.