Although it would be nice if there were more advanced form-initialization functions built in, n8n’s form trigger is a basic, bare-bones, “get things up and running fast” kind of feature. As far as I can tell, there is no way to use anything from the webhook URL (query params) in expressions when the form is initialized. If you wanted to write up a Feature Request, it might be something the n8n team would consider adding. Be sure to look through the existing form-related feature requests first to see if anything already describes what you need. This one seems similar to me, so you might just add a comment there, and vote on it.
If you need more advanced forms, there is also a trigger node to integrate Form.io, which offers a broad set of web-form feature support.
Check into the Form.io cloud/hosted service, and/or the community edition of Form.io to see if that would help you accomplish what you want. There is also an online forms builder where you can experiment a bit.
If this answers your question, please mark this post as the Solution.