How about change of file type for list of files?

[Jari Häkkinen]

Add support to change file type for files selected in the file viewer, I assume a button with a proper action is needed for this.

Some quotes from the linked mailing list thread below

A workaround is to match file extensions to MIME types that
are linked with file types.

It does make sense since MIME types provide only partial solution (non-generic file 
extensions) and looks to me as a good solution.

Refs to ​http://www.mail-archive.com/basedb-users@lists.sourceforge.net/msg01699.html

[Nicklas Nordborg]

Replaced by #1579.