Hi tricon
To change this individually, you can change the value for PLG_JOPENSIMREGISTER_OPENSIM_DETAILS in the file /administrator/language/en-GB/en-GB.plg_system_jopensimregister.ini
Mind that when updating the plugin, this value gets overwritten again. Alternative you also can create a line with this in /language/overrides/en-GB.override.ini so you will keep your custom value even after updating the plugin.
Greetz
FoTo50