I don't "think" PD lets you select chroma subsampling.... but....

PD lets you create customs profiles that expose some (but not all) of the variables that can be used by the encoder. These details are then held in a text file but expose more variables that you can then modify by hand.

For example,
a) Go to the produce tab as normal and select say the the AVC 1920 x 1080/50 or 60P (28Mbps) the press the "+" button to create a new Profile.
b) Give it a name and description that you like
c) Close PD12
d) Open this file in Note Pad: "C:\Users\[USERNAME]\AppData\Roaming\CyberLink\PowerDirector\12.0\Profile.ini

You will then see a range of items that can be modified by hand (such as GOP Stuctures) etc. I can not see anything obvious for Chroma Subsampling in this list but some of the Fields and their values are "vague" so you could experiment to see what changes to these values correspond to changes in a subsequent output file.

Thanks
Nathan PD 64 Bit-Win10 64 Bit-32GB RAM-80TB HDD
Sony FX6 - 500Mbps 4k/50p AVC-I HLG
Canon XF400 - 150Mbps 4k/50p AVC
GoPro Hero6 Black
Pana HS700-28Mbps 1080/50p AVC (High@L4.2)
Canon HV20-HDV 25Mbps 16:9 1440x1080/25p MPEG

Thanks Nathan. I will give it a look.