In all screens I will be giving the option to set both the tool number and the offset. This will allow you to do whatever method you desire. If the offset is 0 it will be set the same as the tool. this should make everyone happy.
As I previously said, just make sure the name of the tool is tied to the offset number (yy in Txxyy). I think it wouldn't affect the new tol numbering while it would be beneficial for the old one.