Hey
It should be possible to switch a texture during runtime however it would not be an easy task. To do so you would need to set up a dynamic material instance and then change the texture parameter. If the texture being used is saved outside of the project then you need to hardcode the path to the texture. If the texture is saved on a web server you would need to include the URL to the texture as well as make sure that the game is able to connect to the internet to retrieve the texture. Depending on the number of images and reasoning, it may be a better option to bring the images into the editor to make referencing them easier.
Cheers