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if you need to have a test system to manipulate your files for testing for EVAs, SANs, and XPs, I suggest you create multiple vaults at a certain size so that you can mirror/snap/business copy production to test and the last vault is the incremental which is really fast. This way it is a way to play and test without any issues of read only when try to delete or testing other issues like removing unreferenced files. You can keep the old vaults as read only and have the EVA/SAN/XPs move the data over to archive areas to save money.
I do like Tony's idea of read only if you don't have the abiltiy above since EVA and SAN space is expensive. For those who don't even externalize their data into vaults like some companies I know, just do the same as above with your tablespaces and reinitialize your oracle with the correct hostname for the database.