Out of desperation i've created this tool to shift the timming of BD subtitles in sup format and i've called it SupMover.
It doesn't do much cheeking of input file or the inputted parameters (yet, as i expected to not distribute it).
Here the repo
https://github.com/MonoS/SupMover/
EDIT: after a couple of years i took the time to add some new functionality to this mine little utility, now it can resync subtitltes and crop the picture area without reencoding the picture data.