The Nuvi 2x5 series does not support custom routes - see this:
http://forums.gpsfiledepot.com/index.php/topic,687.0.html. But the Nuvi 5x0 does - you can use Mapsource on your computer (if you have City Navigator installed) to send routes to it.
I also have a Nuvi 205 - are you really seeing an "active route" in current.gpx? If so, that's interesting. Regardless, there isn't going to be a way to send it a route. Current.gpx is only an output file, the actual data (waypoints and tracks) are stored internally in an area where you can't access them. Everytime you startup the Nuvi, it writes a new Current.gpx file which contains the latest set of waypoints and tracks. Changing this file should have no effect on the internal data structures.
However, if you put waypoints in a file named temp.gpx (or actually anything.gpx EXCEPT current.gpx), the Nuvi will read it when it boots and add the waypoints to the internal data. You can use mapsource to send routes to the Nuvi 2x5, but they will not be accesible on the unit since that feature isn't supported.
You can also send tracks, either with mapsource or temp.gpx, but they will not display on the unit. The only tracks which you can display are the active ones which were recorded on the Nuvi. This is one reason why you should think carefully about whether the Nuvi 5x0 will really meet your needs for hiking. Handheld models have much more support for this kind of advanced feature.