Can I disable access in OneClick for users or groups to the Telnet function for devices?
Yes. If you want to remove the telnet function for a specific user when right clicking a device you can do this by modifying the group or user permissions.
From the users tab select the user or group and then from the component detail pane select privileges and click add /remove.
From add / remove privileges expand tools and then uncheck telnet option. This user will no longer have access the telnet option when right clicking device.
Note: You can also modify custom created roles that are assigned to users in the same way by editing the role.