If the Guacamole login name is stored in an environment variable or registry key, you can configure Veyon Service to read this variable/key and provide it as session metadata to Veyon Master. Then in advanced view mode in Veyon Configurator you can change the "Computer name source" to "Session meta data" and should then see the contents of the variable/key instead of the computer name below the thumbnail (requires Vexyon 4.9.3 or newer)