There is a setting For Mach3 turn to use a REAR toolpost. This will do what you want. Check the manual.
(;-) TP
All I could find is tool table in manual by searching rear tool post so I was thinking that I need to change definition of tool (I am still cutting air so do not have tools), anyway I found one topic accidentally , on some old forum and solution is to check only one box, I thought it must be something easy , just did not know where to look any more. Any way thanks, I appreciate when somebody try to help. I already got new question what I need to ask, how to rotate tool path, I figured out how to zoom it and move it around, I before 2 years manage even to rotate it (because I had some old version of Mach 3) and today while I was reading manual, I read you can rotate tool path and I can not succeed to do it, and I was watching picture of machine piece that is rotated, so I was thinking I need to open new topic because I can not to do rotation.
Anyway I read again on some old forum that in newest version of Mach3 that is not possible, I guess it is true

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And yes here is how you invert tool path:
https://www.youtube.com/watch?v=e_9HAffmyao