Yes if you can remove the seat and re-do it. Or you can get seat pads that fit and attach them to the seat (or leave loose).
It will depend on the chair you have. Many times the cushions can be unscrewed from the bottom and recovered.
This video shows you how to recover them, so you can probably add new padding during this step as well: https://www.youtube.com/watch?v=FsPQQQ9flG4
What type of folding chairs do you have? Please post a picture so that we can see what you are starting with.
Hi, I found this video that will show you how - https://www.youtube.com/watch?v=YSqBhoXQFNM
Yes definitely. It is just like re-upholstering any other chair but probably easier since you have such a flat pad to work with. Look for the screws in the back of each section you want to remove. Remember how it goes back in. Check out my post to get you started:
There are lots of folding chair ideas here for you to look at also:
This is a good tutorial: https://youtu.be/d8mDwtak9nY
Here you go. https://www.hometalk.com/4979139/folding-chair-makeover
Do you have a picture of your chair?