[exim] return value from external script

Hi

Can you please help me to find a way how to configure exim make following
things:
1 send whole message to external script (application)
2 return a value from executed script to a variable

I found that i can use pipe in filter with unseen option. In this case i
can add custom X-header, re-inject message to exim and play with X-header.
But i do not like to re-inject message from script.

I found similar actions in wishlist (195).
If you know if i can implement that please explain me the right way.

Thank you.
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