Well, it really is just that simple. Just tested the macros, and it all works just as it should you can actually define the tools any way you like, but for safety sake, it really is best to make an offset of 0.000 correspond to your longest tool, so there's no danger of a crash when you turn comp off.
The macros I'm now running are below. M843 applies the comp, M849 removes it. Use these in place of G43 and G49. With M843 use the P argument to specify the tool table entry whose length offset is to be applied. You may find the "extra" moves in there confusing - I do this because I have a lot of backlash in the knee - bevel gears and a leadscrew, rather than a ballscrew - so I get most repeatable positioning by moving the knee up to final position. So, if a down move is required, I move down a little past the target position, then back up to the target position. This gives me excellent repeatability.
Regards,
Ray L.
Oops! Posted the wrong M843 macro. Now fixed.