As far as i know, for pillow to do what you want you would need to
- Take a gif and split it in to frames
- Edit each frame individually
- Put frames back together as a gif
- Repeat for every gif
It can be done automagically like you want, but if you’re not interested in learning python maybe the XnConvert or ffmpeg comment above might be the way to go for ease of use.
If you can figure out some way to upload it to your desired destination and get a link to it, maybe this bot can help you post on lemmy at a specific time of the week/day.