Absolutely, here's how to do it. First, you need to log into your Twitch account. Then, go to the 'Creator Dashboard', you can usually find this in the drop-down menu under your profile avatar. Here, select 'Channel' under the 'Settings' menu on the left side. There will be an option titled 'Video Player Banner'. You can upload your desired offline screen here. Be sure that the image complies with Twitch's policies and is the correct size (1920x1080 pixels). Once you're done, just hit the 'Upload' button.