Hello. This is a simple interface request. In the tree panel, if you drag an image from the images folder onto an existing slot, it adds that image to the slot. This is the expected behavior. However, if you activate the slot and attachment filters for the tree, you can no longer do that. You can only replace an existing image.
It would be nice to have this work the way I envision it should. The tree gets super long with the bones visible and that means a lot of scrolling up and down. If there is a reason for it to be designed like this, please let me know. Thanks!