Pixelfed supports tags, so even if the official team didn't want to do that, it should be possible to make an alternate front end with different tools to allow you to categorize pictures in other ways without having to interfere with the actual mechanisms/structures storing pictures.
It would also be perfectly possible to branch further from Pixelfed, but still keep compatibility federation-wise to leverage the social stuff. This would, in theory, allow you to focus more on the portfolio aspect on your own site, while still also having the social feed portions for people to follow your work in real time. It might be easier to implement something like requiring moderator review before a comment on a picture displays with a harder fork.
That's all way past the scope of what I'd have time for, though. I'm more likely to make something simpler from scratch that fits my own criteria.