Hi,
you question need to be more specific if you wish to have precise and usefull answers.
There is no way to get both HR/LR tex in one tex file, but you can do two archives, one with HR tex and the other with LR tex and use one or another in the track file ('trk' or 'scn' or other track file).
For info about DDS format and the different compressions, look on wikipedia or directly NVidia developper doc which comes with nvdxt tool.
example http://en.wikipedia.org/wiki/DXTn
Regards.