Rush Javascript Programming Needed

We need some javascript written for a rush project. The javascript will swap out several html form field elements based on which radio button a user selects from 3 different options. We have pre-determined html form code all set to go. We just need someone to create the javascript code to swap out certain elements in the form code based on the radio button selection so it submits correctly into our our 3rd party CRM. The javacript should NOT swap out the entire form. We want the form fields visible to the user the whole time and don't want the form design to change. The javascript just needs to sub out variables inside the html form code. So nothing fancy, not ajax, just simple javascript. For someone that knows what they are doing its probably 5 lines of code.