launching "bootmii" via the HBC (or generally anything) will only work if SD:\bootmii is saved to your sd card. If you use modmii, it will put that folder on your SD card as well as have you update priiloader, the hbc, etc.
Since you already have homebrew, the easiest way for you to update your softmods is to run syscheck on your wii, than drag and drop your syscheck.csv onto modmii.exe and it will generate a custom guide for you to follow to get yourself all up to date. Note that it will see that priiloader is already installed and not instruct you to update to v0.9 (syscheck doesn't inform us what version of priiloader is installed).
Alternatively you could just run ModMii's main wizard as if the Wii was a virgin, and follow the guide, repeating steps even if they seem a bit redundant, redoing steps is fine, but skipping the wrong step is not