As can be seen in
RatesCalibrationCsvLoader the calibration file format is not extensible. Strata does not include Fixed-Float Cross-Currency swaps as we understand these contracts to not be particularly standardised.
There is no need to alter the
Swap class or the analytic pricing modules - they all handle cross-currency swaps fine. What you do need is to add new instances of curve node, convention and template, probably based on
XCcyIborIborSwapTemplate. If you were to create these classes, then you could create your own input to the calibration process using
RatesCalibrationCsvLoader as a guide.
Hope that helps