Once you format your sd card and do as it says below in the spoiler those wads(58/61) will install to the wii's nand.
It's always good to make another back-up of your nand with bootmii, but yes you can just install the HBC and exit the Hackmii installer.
Please read the guide a few times, then proceed.
Softmods with HOMEBREW CHANNEL installed
If you already have a softmod with HBC installed, you can update your softmod with this guide.
Note: 4.3 wiis can skip installation of ios58 and 61, and simply load Hackmii from the HBC.
Backup and Format your sd-card
Extract WiiMod-58-61_Hackmii_1.1.0 to sd:\
Load the HomeBrew Channel
Launch WiiMod - WiiMod will load
-Select Wad Manager -Press A
-Press 1, -press A -Install all wads
-IOS58 and IOS61 will install
-Press "any button" to continue
-Exit WiiMod to go back to the Homebrew Channel
-Select hackmii_installer_v1.0 - Press A to Launch
-Hackmii Installer Loads