Rapture Session Chemtrail Bass

I loaded Chemtrail Bass into Rapture Pro (it comes with that as well) and this patch is indeed tuned a semitone down there as well. Of course, Rapture Pro does allow you to make the adjustment.  As you have Rapture session only, I don't think you can adjust with that

However, rather than transposing the MIDI note events in the track, you could raise the key of the entire MIDI track by a semitone using the MIDI track inspector Key+ setting.  This is right above the patch browser.  That way, the notes will be correctly displayed in the PRV and Staff, but the patch will sound the correct note.

Hope that helps