Different defaut field value for each helpdesk form?

Hello, I'd like to have multiple helpdesk forms for different usages like: bug report, question, offer etc. And I'd like them to have a field like “type” that would be pre-filled based on what form it is. E.g. a bug report form would have “type”:"bug report" by default and a question form would have “type”:"question" by default. I can't just use a normal dropdown selector with all the options because I want this “type” attribute to be unchangable by whoever is using the form. Like this form is for bug reports only or for questions only etc.