So far there is no sign of a way in for the more recent Humax PVRs, for inserting code. The best that has been done is to reach in through FTP and manipulate recording properties so that HiDef recordings become streamable and decryptable the same as StDef recordings (on the HDR-2000T - even that may not be possible on FVP-4000T).
The security on the firmware download format for FOXSAT-HD, FOXSAT-HDR, HD-FOX T2, and HDR-FOX T2 was possible to analyse and recreate to then be able to build "fake" firmware update files. The security has been tightened for the more recent models, and although it is possible to read the downloads, it has not been possible to recreate the authentication that they require to accept a modified update file as valid.