Hi Oldden,
I only know the following method to assign a new/own Icon to a (non-protected) pack:
In My Packs, select the pack and then click on it a second time. A dialog window "Pack Property" will appear in which you can select the desired image file (e.g. in .jpg or .png format) for the Icon.
To assign a specific Yamaha Icon to a Voice within a pack, select the voice in the currently selected pack and then click on the voice a second time to open the "Content Property" window. Then select the desired keyboard model in the dropdown box and then click on the "Select Icon".
Best regards,
Chris