I got this reply from George when asking a similar question (apply merohedral twin law to HKLF5 data):
"I would simply write a (trivial) program to read the .hkl file and expand the two components for each observation to four copying the intensities and using the appropriate matrix to transform the indices, and set the twin component numbers 1 to 4 rather than 1 to 2. The first three contributors should have negative twin component numbers and the fourth should have a positive number."
That worked reasonably well for me, R values did increase though as predicted by Oleg
you could give a try to olex2-refine. We did implement this quite a while ago, look here for the relevant discussions:http://www.x-rayman.co.uk/xforum/viewto ... 122&t=1467
People however find it not much exciting, since using more data increases the R-factor values