Gmail – In Gmail, how does one change the appearance of action labels at the top

In addition to the good options Ian offered of dragging labels to the emails and using the list with the mouse as a multi-selector, there is also a way to speek this up with the keyboard.

While typing labels you can accept the current one by pressing enter instead of switching to the mouse to click. You do NOT have to even type the full label, as you type the nearest match will be accepted on enter. If you have keyboard shortcuts turned on in your gmail you can label any open message or selection of multiple messages by pressing the l key. If your labels are unique enough that they don't usually share a first letter, this get's all labeling operations down to three key strokes. l > X > Return where X is the first letter of your label. L enters label mode, start typing until you have a label match, then enter to accept. Repeat to add another label by hitting L again.

I'm not entirely clear on what you're trying to do here. If I'm reading you right, you want to create a new email address for yourself without telling the people with your old email address the new one. I presume you also want to keep getting their email messages but don't want to have to log in and out of two Gmail accounts constantly.

This is what I would do:

1. Create a new Gmail address/account
2. Set the old address to forward all mail to the new address (Settings | Forwarding and POP/IMAP)
3. Set the new address to be able to send email as the old address (Settings | Accounts and Import | Send mail as)
4. Create a filter to make all messages to the old account (and which are now auto-forwarded) go in to a special label so they're easy to find

One downside of this is that Gmail includes an "on behalf of" message in the headers of the messages you would send from the new address as the old address. If you want to avoid that you can log in to the old address to send your replies. Google's Multi-Account feature makes this pretty easy.

Of course, all of this is unnecessary with several of the desktop mail clients that are out there.

If this isn't what you're trying to accomplish, please update your question to make it more clear.