Sorry to revive this old thread, but since this is the main result for a Google search for “Renoise rx2” I thought I’d share the answer:
https://www.renoise.com/tools/additional-file-format-import-support (Renoise < 3)
https://forum.renoise.com/t/new-tool-recycle-rex-files-4-renoise/30399
Would be cool to have the format input support tool updated.