Yes it is possible, it's a bit complicated, but it's possible.
Do the following:
- Export your database (it is suggested to)<br>
- Delete all songs
- Click Extras > Open File Structure...
- Open the "songs" folder
- Close OpenLP<br>
- Delete "songs.sqlite"
- Open OpenLP<br>
- Reimport all songs (with the fixed charakters)
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This way, the whole database is rebuild, incuding all authors, themes and song books that are written in the reimported xml files.<br>