It will require a logic and a dictionary on which this will work. Better use VS Code and search for all words that you need to change with case sensitive and replace in bulk. That will be way quicker.
I have a similar approach on one of my sites - I store the tags as (mostly) lowercase, but every now and then I have something I want capitalised, so I store the tag in the frontmatter exactly how I want it displayed. Then, when I render the tags in my template I use a Hugo function (title) to capitalise, but because you can’t capitalise something that’s already in caps, my tags that I pre-capitalised are unaffected.
Here’s an example of the template (ignore the classes, they’re not relevant):
<div class="item-taglist">
{{ range sort .Params.tags }}
<span><a class="tag has-background-dark has-text-white" href="/tags/{{ lower . | urlize }}">{{ title . }}</a></span>
{{ end }}
</div>