For radios with firmware version up to and including v265 I think Sharpfin is a better solution. Once Sharpfinned, presets can be loaded using a web browser pointed at the radio's IP address. Entering the preset details is not dependent on Reciva servers so can be done at any time.
On my sharpfinned Tangent Quattro, presets are stored as xml fles (presetN.xml) under /root/config/. I played with them years ago, when I even made a toy
preset browser plugin for the sharpfinned radio.
However, AFAIR, unfortunately one cannot just edit the url inside the preset file to a new one (that would be telnet/vi, or was here ftp?), and have the preset work. These xml files have the form
<preset od-starttime="0" type="PresetType:Internet" id="5" stream-id="2149"><station id="2765" custommenuid="0"><version>5127</version>
<data><stream id="2149"><url>http://radios.argentina.fm:9270/stream</url>
<title>La 2x4 Tango Buenos Aires</title>
<protocol>http</protocol>
<metadata><use-metadata author="true" title="true"></use-metadata>
</metadata>
</stream>
</data>
<genres>23</genres>
<locations>34</locations>
</station>
</preset>
and probably fields like <stream-id>, <station id> are critical and depend on the reciva server. I don't remember what was the effect when I changed the url with another working url in a given file, but if it was working, I'd have made that editable. Maybe I'll give a second try somewhen.