For some apps a simple change to the bootstrap URL should suffice. For others, it depends on the libraries that are being used ... there are a few currently not in the OpenUI5 version. You can get a quick overview of the differences by comparing the API symbol trees between
https://sapui5.hana.ondemand.com/sdk/#docs/api/symbols/sap.ui.html
and
https://openui5.hana.ondemand.com/#docs/api/symbols/sap.ui.html
cheers
dj