How do I change my personal Mii on the 3DS?

I imported my old Mii into the 3DS from my Wii. Now, I'd like to replace the "personal Mii" that I set up on the 3DS with the one from the Wii. Is there any way to do it, without editing the existing Mii to look like my old one?

A valid workaround would be to let me erase all my Mii data (but not the purchased games on the system), and start over with an import.

Hopefully, this describes what you want to do. From Nintendo:

How to Change the Mii Character Used in StreetPass Mii Plaza

Important Note! Only a Mii character that was created by the user can be used as the display Mii.

What to do:

Select StreetPass Mii Plaza on the HOME Menu, and tap "Open."

Highlight your Mii Character and press the A Button.

Select "Mii Settings."

Select "StreetPass Setting."

Select "OK."

Choose Mii from the list of Mii Characters. Select "Yes" to confirm.

Note: This is the only Mii you can change - you can edit your personal Mii, but you cannot delete it or switch it for a different Mii you have created. (It actually warns you about this when you create them, and also in the manual.) Also, if you attempt to delete them, you get a message that says "Your Personal Mii cannot be erased." You can re-format the 3DS, however, in order to create, effectively, a blank slate for yourself, but editing the Mii is really your only option if you do not wish to take that route.

If you want to reformat the 3DS, go to System Settings -> Other Settings -> Format System Memory (it is the last option on the 4th page.) The following information will be lost after formatting the system memory:

• All data in the System Memory (including Friend List, Notifications, and step count)
• System Settings data
• Built-in software save data
• All photos in the System Memory
• All other extra data (created by some games and applications)

It will not, however, delete your e-shop account.

Just edit your main Mii - that's what I did :p

You can change the creator of the Mii, and then erase it - that's what I did and it worked fine.

If not you can just edit your Mii!