There is already a dialect file for XC= BASIC (open a .bas file and select XC= BASIC from the drop down).
You will need to create a solution/project. Add a new .bas file to the project. In the project properties you can add either a custom or a post build event to call the XC= BASIC compiler. I’m not up to date with its call syntax but it shouldn’t be too hard finding out.
The help/manual of C64Studio (F1) is also available online at: https://www.georg-rottensteiner.de/c64/C64Studio/manual/main.html
The description of the build events is found under Build Setup->Build Steps
HTH, otherwise don’t hesitate to ask!