Hi Ralf,
It is not possible to change the fonts encoding of the barcodes produced by PSM. Amongst other things, they aren't drawn using fonts, but rather using a barcode plugin called by the barcode object. If your barcode isn't in the list of supported barcodes, you won't be able to use it. (unless you have a font for it, then you could try to make it using text and a barcode font, but we don't really provide support for third-party barcode fonts, so that may or may not work)
Regards,
Raphaël Lalonde Lefebvre