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I personally would not directly link "Parametric" with "MACRO". But it may be that you require MACROS to do Parametric programming.
What is your understanding or definition of Parametric Programming?
MACRO in the CNC field is quite different than MACRO in the computer field. In the CNC field MACROs are an extension of the standard G & M code program language and may provide variables, functions that can be performed on the variables, parameter passing to subroutines, and some special functions like DPRNT.
My definition of parametric programming is where you create some general sub-program for a particular class of applications with variables in the sub-program that you can provide specific values to at the time of execution of the sub-program to make a specific part or pattern.
So long as you have the ability to use variables then you can do parametric programming. Your test of #101 = 1 with no error seems to imply "MACRO" capability. Proceed a little further and try something like the following in a program.
#101 = 1.0
#102 = 5.0
G00 X 0 Y 0
G01 X#101 Y#102
Use whatever values you want and see if the machine does what you expect. Obviously you need initial and ending code.
G65 is a sub-routine call that provides a means of putting parameters on the calling line.
If you do not have a manual, then download a copy of the HAAS mill manual from their site. This manual is 96-8000.pdf .
HAAS to some extent copies Fanuc and HAAS variable numbers may give you a hint.
What is your vision of how a parametric program would help you set tool lengths? Do you have a probe of some sort?