With only 10 objects, I think the easiest way to accomplish this would be to add the text block, copy and paste each object's XML Block into the text block, then remove the XML block.
As an aside though, it might be a good idea to leave it as an XML block, even if you don't think you will need it now. The problem might be turned around in the future when it would be harder to convert it back.
There is little downside to using an XML block vs. a Text block that I know of.
After your suggestions (which I find both true and valuable by the way) as well as few experiments of my own, I'm starting to face the fact, than planning would be everything in custom class use and eZ isn't as flexible as I thought (even though it is still far more than I have ever expected before I started using it) :)
This is not a standard feature of eZ publish, but some time ago I've made an extension with a GUI for datatype conversions. It uses a plugin system, so every possible datatype-to-datatype conversion can be supported. The quality of the conversion depends on the plugin.
You can download a first alpha release at http://ez.no/community/contribs/datatypes/datatypes.
