The process of accessing another account object via the Multilogin method will not update the appearance of the client. Account objects, whether they be the root account, or obtained by calling Multilogin, are opaque, and have no affect on the appearance of the client.
The only way to have the client change in appearance is to use proxy. However, the applet you are modifying was written using the account approach, which is the most efficient way to access data in the GroupWise message store. You could probably rewrite it using proxy and commands like GroupWise.ItemListCreateFromView(), but this would be a big job, and probably not worth it just to see the client change while the data was extracted.
If it is important to see the client change while the export process takes place, you might be able to proxy to the appropriate user, then use the multilogin feature to access the appropriate account. After you have exported the data, proxy back to the root account (and release the account object you obtained in your call to Multilogin).
I hope this helps.