How to write custom fragments for inclusion in macros and dialplans?

Colleagues, tell me, please, what am I doing wrong - custom fragments written by me are not added to the beginning of the dialplan code.

I want to add a custom snippet to the top of the macro-auto-blkvm macro. I believe that this desire is quite innocent and permissible. Moreover, at the beginning of the macro there is a line intended for this:

include => macro-auto-blkvm-custom
exten => s,1,Set(__MACRO_RESULT=)`

How should the code be correctly composed in the context of macro-auto-blkvm-custom so that it starts executing at the beginning of the main macro?

In theory, a forbidden situation arises - in the same context, two lines appear with the same extension (s) and with the same priority - 1.
How will Asterisk resolve this contradiction?

Grateful for the replies,

Is there a reason this is a new post rather than continuing your previous post?

This question of mine is a special case of the big question in the post you pointed to.

Unfortunately, I did not receive an answer to the question asked, perhaps my colleagues did not pay attention to it. Perhaps this question is very banal for everyone, but I did not find an answer to it.

Also, this post contains a question about two lines with the same extension and priority, which was not in the previous one.

Therefore, I asked the question, not because I have nothing else to do, but because I need to get an answer to it.

Did I understand correctly that you will say something about the essence of my question?