Quote: My camera shoots 1920x1080 50p at 50mbs using the new XAVC S codec

I would like to burn BD's at this higher bitrate, but can only see a 28mbs option available for BD

Is there a way if keeping my original 50mbs bitrate when producing the video at 1080p ?

In the future maybe.
http://en.wikipedia.org/wiki/Blu-ray_Disc#Ongoing_development

Current Maximum bit rate for BluRay.
Bit Rate:
http://en.wikipedia.org/wiki/Blu-ray_Disc#Bit_rate

You can get a higher bit rate with software other than Cyberlink.

Carl312: Windows 10 64-bit 8 GB RAM,AMD Phenom II X4 965 3.4 GHz,ATI Radeon HD 5770 1GB,240GB SSD,two 1TB HDs.

Quote: Is there a way if keeping my original 50mbs bitrate when producing the video at 1080p ?

If you mean producing a video file (as opposed to burning a disc), the answer is yes.

Once you've selected the format & 1920x1080 (28MBps) profile, click on the + button to set the VBR up to 48.5MBps.

The "backroom" alternative is to edit the Profile.ini, where you can set the VBR to whatever you wish.

Cheers - Tony
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If I may pop in about this, with a little suggestion (although the ability to Produce at higher bitrates has been explained, and one of the reasons why given, from two very knowledgeable people here):

If you are producing video that is going to be enjoyed at home [for instance], or is going to be played on a full desktop system (or HTPC, or powerful-enough laptop at work, etc) may I suggest that you produce the video at your desired [high] bitrate, and simply write it to a disc as a file (Data Disc or on to a Flash Drive or a Portable Hard Drive). Doing this, you can maintain the high quality level that you may be desiring, as the hardware will then be capable of playing back the high bitrate data file (it won't be limited by the attempt to keep the lower-bitrate 'Standard').

The bitrate limitation is not due to PowerDirector specifically, but due to the standard, which normalizes specifications to allow for all machines ("BluRay Players") to have the same capability [of the same hardware]. That way, if anyone takes a BluRay disc they created to any Standalone BD Player, they can be more certain that they will be able to view and enjoy their disc. PowerDirector's conservative 'suggestion' of writing only 28Mbps is just to ensure that any output/disc created will not have a problem in almost all BluRay players. Most players have hardware that is capable of the Standard bitrate, as far as output and read speed, and some even have a bit of 'elbow room', allowing for spikes of up to 70Mbps or so (depending on the video buffer and power of the chips inside); but for the most part, any limitation of ability is because of the hardware in the majority of players - simply not having enough computing power, or 'restricting' themselves to the standard.

One last note:
If you end up writing your video to disc with a very high bitrate - one that exceeds the read speed of your disc drive - then you may experience lag or 'choppy-ness'. If you do, then merely copy the video file to a faster drive (HDD/SSD/etc) that allows higher throughput. Then, you can be sure you will be able to play back your video [on a powerful enough system] without any stutter, lag, etc.

Sorry that turned into a longer 'little suggestion' than I originally thought, but if you write your videos to disc not as a BluRay (BD format), but as a Data File (.mp4/.m2ts/etc), then you can play back your higher bitrate video and enjoy it that way, in the end.

Good luck with it and have fun!