If I’m reading your question correctly, it sounds like you use a tag for each client, and you want an extended client description to show up when viewing any topic having that tag.
It’s not a form really, but the Tag Banners component, as seen here on Meta, might get you halfway there:
With this component installed, you can add a text description for each tag that will appear in a banner shown when the tag itself is selected. The text field takes HTML and can be styled with custom CSS so you could do quite a bit with it, but here’s a very plain example where I’m editing a tag:
The challenge would be to alter this component so that it shows up not only on the tag page, but on each topic using that tag. I don’t know how much work that might be, but a more experienced coder (like Nate…) might have some idea.