Modification of code G33.1

Hello everyone,
It is my first post, so welcome 
I am new in CNC and I want to support my friend that have bigger experience in CNC but is not software developer.
I hope it is correct forum category for such question.
General question is: how can I modify G33.1 code cycle to avoid last change reverting rotation of spindle. 

In details :  as I understood G33.1 code is for rigid tapping and my friend wants to modify it because he did not find another solution.
Cycle works in following way :

0. when it is in right position
1. starts tapping with appropriate speed
2. when reaches required deeps, spindle changes rotation to the opposite and moves back
3. when it is outside the tapped hole, spindle changes rotation to the opposite and finish

So in our case last step 3. is not necessary and we want to eliminate it.  Ho can I achieve it ?

After digging in documentation and forums I found that I can change axis because axis UI parse program (g-codes too) so, from architecture diagram I found that it sends its to few modules. So theoretically g33.1 code is some NML messages pack, so I could change interpreter.
Another approach is to remap function (I absolutely don't know how to write it ) and create new one  e.g. g33.2 that will be do only what is necessary.  
I created VirtulalBox machine,  installed LinuxCNC, examined (less more) how /usr/binlinuxcnc  bash script that start everything but failed how to debug axis python code.
So I decided to ask here
please help
Regards,



 

See if section 7 in this document is of any help:

linuxcnc.org/docs/html/remap/remap.html

thx for fast response;
I am able to solve my problem using remap and new code ?