Of course you can.
To make the transition as smooth as possible, we recommend that you start by uploading the release with us, then remove it from the other distributor.
And if you send our support team a screenshot of your take-down request, it will speed up the review process.
You will also be able to use your old ISRC codes for your new release on Record Union. Just add the codes in the ISRC code section for your new release and your are set to go.
Using your old ISRC codes will make sure that the public play statistics on Spotify will stay intact.