It depends how long you have had them online. Apparently after 30 days online, AS keyword order is pretty much locked.

Mat told in the past answer to similar question: changing title and keyword after the images are online is always possible but this gives minimal change in search ranking if done after some time, more than 30 days, so probably not worth it

I do, occasionally, add to keywords if I realize I forgot something important. Being found is one of the important elements in licensing your work, and regardless of order, if you don't have the keyword, your image won't show up at all.

Sometimes I realize I need an additional term for the same thing (this doesn't apply for iStock/Getty where everything is reduced to the controlled vocabulary anyway). As an example, years ago I was putting remodeling in for all the home remodeling images and not, initially, renovation when that applied to most of the images as well.

Trying to game the secret sauce of search order seems not to make sense when we have virtually zero data to work with. I do put the important keywords first as that's never wrong on any of the sites.