I made a custom template for dita.pdf2 which i set up in transformation parameters as "customization.dir".
I'm happy with how it's working, but now I need to use same customization to export document in DOCX format.
What are the easy ways to do it or should I start from scratch and use different scenario?
You cannot reuse your pdf customization for the Ms Word output. The way in which you can customize the ooxml output is by creating a template ooxml file: https://github.com/jelovirt/com.elovirta.ooxml/wiki/Extending