Duplex printing options using lp or lpr

The right place to set options for the (/this) printer, is in /opt/brother/Printers/mfc9340cdw/inf/brmfc9340cdwrc. The problem of always resulting in a DuplexTumble printing, was forced by the respective code-line (BRDuplex=DuplexTumble) in this configurations file.

Setting the option in question to BRDuplex=DuplexNoTumble, and restarting the cupsd service (in my case, using rc-service cupsd restart for OpenRC) results in double-sided prints binded along a document's long-edge.

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I came up to check for a file named like br(model name)rc only after reading this section of a relevant Ubuntu-Wiki page: http://wiki.ubuntuusers.de/Brother/Drucker#Problembehebung