To have the new meaning be specifically about the project files and their (raw, XML) content, their creation, manipulation etc.
- introduce the new tag name qgis-project-file that makes this intended meaning more obvious
- make qgs and gis-projectqgis-project synonyms of that tag
- remove gis-projectqgis-project (and qgs) from questions that are about the general QGIS concept of projects but not about those projects on-disk representation or its manipulation. qgis should suffice for those questions, as you can't really work with QGIS without a QGIS project anyway.