@nmorin - In order for the file to be replaced, the size needs to be different. So you could simply make a quick optimization to the asset, then upload it again. Renaming won’t change the same asset on the CDN. After uploading a new “version”, you have to swap images in the designer since there is no replace function.
As for SEO and Images in general there is a very informative resource Google provides which is “Google Images best practices”, as an SEO practitioner it’s worth memorizing.
Google Images SEO Best Practices | Search Central | Google Developers
In response to a question about SEO and images (11/07/2012) titled " What should filenames and URLs of images contain for SEO benefit?, Google’s John Mueller said
" From our (Google’s) point of view, you can use whatever file names & URL structure that makes sense for your site – you definitely do not need to fine-tune it on this level for SEO purposes. For Image Search, we recommend using descriptive file names, but even if it’s just a number (for example, when a photographer uploads files without modifying the file name the camera used), we can usually work with that just fine - we use a lot of signals to pick up information about an image."
Here is a timely article that is worth a read by Anna Crow. Anna is the Assistant Editor for Search Engine Journal and Head of Content at Leadfeeder. Over the last 10+ years, Anna has successfully been running her own SEO and content agency working with brands like Moz, Kissmetrics, Dollar Thrifty Rental, Hearst Magazine, Mailboat Records, Philip Morris International, Bloomin’ Brands, & many more.
11 Important Image SEO Tips You Need to Know (searchenginejournal.com)
My personal SEO experience shows that using folder names in paths (relevant) that group images into categories helps for Image SEO and since images are often linked, and this benefits the site and image search traffic.
File names can be very important. As a photographer I always include my name in image files since EXIF info can be stripped out. When doing product catalogs good file naming has been huge for SEO / traffic from image search. Basically as a site owner you have to take advantage of everything you can.
Good news is in Google Image Search , images on the CDN are correctly attributed to the site they were crawled from including both domain and the page.