When you use the Custom Names feature of Plus!, you can set a custom name for them, which will show up in your contact list (and conversation window, if you want).
Go to Plus! > Preferences > Contact List > Custom Names and change it. You can use tags as (!N) for your contact's display name, and (!M) for their email addresses.
A limitation of this feature is that emoticons will not show up in your contact's display names in a conversation window anymore. A way to avoid this is to use custom names without emoticons, and using them in conversation windows too. It's either that, or not using custom names, or dealing with it
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