I have a EPiServer site where I have both english and danish enabled as languages. When I make a non-culturespecific property and create a new page the property is only editable in the language it was created in. Is it possible to change this so that the master language for pages as default are english or to change to the master language after a page has been created?
It is possible, but not officially via UI. There is sql script to do so directly against database. This I suppose is not officially supported either. Use on your own risk :)
Sql script for this. Some roots are here (login required) - https://www.coderesort.com/svn/epicode/EPiCode.LanguageTool/EPiCode.LanguageTools/ChangePageBranchMasterLanguage.sql
If that is not working really well you may try to reach support to get newer version of script.