Many custom tick labelling issues can be solved by using one of mpl.ticker.FixedFormatter, FuncFormatter or even sometimes the FormatStrFormatter. But none of them give access to the offset string. In the simplest case, they could just override get_offset with a function that returns self.offset, which could be set via the constructor or just by attribute access. See e.g. http://stackoverflow.com/questions/29827807 .