There has been a lot of discussion on this topic in the following forum post:

• http://thec64community.online/thread/5/load-d81-images-problem

I'll try to summarise the cream of it when I get a chance.

The basic gist is as follows:

In order to make use of d81/d82 files in BASIC, you have to utilise a quirk in the c64 mini:

1. Rename your .d81/.d82 file to be “THEC64-drive8.d64”, place it on your USB stick.
2. Insert your USB stick into the c64 mini while it is off
3. Turn on the c64 mini, then select the game AVENGER
4. Back out of it and then enter BASIC
5. Then try:
   • See a directory listing with LOAD “$”,8 followed by LIST
   • Load the first thing on the disk with LOAD “*”,8,1 followed by RUN (if needed)

• Load ARMALYTE and jump back into BASIC