After backing up your Plus! / MSN settings you could uninstall MSN 7.5 and download
the new MSN Messenger 7.0 build. If i'm not mistaken Plus! 3.63 still works on this 7.0 build and you will be able to use custom Plus! names.
Otherwise you'll need to update to Live Messenger 8.1 which means you'll need Plus! 4.23, but unfortunately Plus! 4.0 and higher does not support custom names anymore. You could use Live Messenger's contact rename feature, but that means you will have to change the names manually and Live Messenger's contact rename feature lacks functionality compared to what Plus! 3.63 did.
/ 
