Hello,
Modifying the metadata displayed on Item pages is definitely a common request for the XMLUI. It's hard to describe the steps in email, but there is a recent webinar from Terry Brady (at Georgetown) that touches on doing this sort of customization in DSpace 6 - "Making DSpace Your Own"
* Webinar Video:
https://www.slideshare.net/DuraSpace/42418-making-dspace-your-own-webinar-recording
This sort of customization is covered in the #2 demo section. He doesn't cover how to specifically add dcterms fields, but just adding any new field to the Item View. This concept would work fine for dcterms though.
After watching the video, if you have further questions, let us know on this list.