Repetier-Host Config - custom.ini
There are a number of useful settings in the custom.ini file that aren't available in the various configuration menus for Repetier-Host.
The one that got me looking at this was wanting to fine tune the steps for Manual Control of the extruder. They are, by default, set at 1:10:50:100 mm, which was much too coarse for my purposes - particularly when trying to keep the mouse hovering over the 1mm band while peering at the extruder head!
The solution - edit custom.ini (in the data folder on the Windows version).
There's a line which is simply edited to change the values for the steps:
eMoveDistances="1;10;50;100"
The same can be done for the XY and Z axes.