I have noticed that the latest SVN for Pak128.Britain uses the ( and ) keys for changing the level in underground mode. When I tested this, I found it awkward to have to use the shift key, and that they did not always work properly. I suggest that they be reverted to the Pak64 defaults of HOME and END thus:
# sliced underground
toolbar[0][20]=simple_tool[15],9,^U,K
toolbar[0][21]=simple_tool[15],,HOME,I
toolbar[0][22]=simple_tool[15],,END,D