This would definitely be tricky, but I don’t think it’s impossible. One method would be to add a div block and have it sit along the entire bottom of the modal.
Then you can drop in a slider component and set each slide to be something like 10% width so 10 slides will show in the full width slider. From here, you can drop inline images into each slide of the slider. Then, you can create an individual interaction for each thumbnail that, when clicked, will bring up the correct main image.
Definitely complex build, but it may help you here!