Customize "Tobacco Use" field only for contacts in VBS

Summary:

Need to make the field "Tobacco Use" "read only" only for the contacts

Content (please ensure you mask any confidential information):

We need to make the Tobacco use field “read only” only for the contacts if employee tries to update the field’s value for any of his/her contact. When they are first adding their contact, they should be able to input a value in this field. Has anyone been able to achieve this?

Also, we noticed that you cannot go to “Before you enroll” (Adding a contact) page in VBS. The option itself (Edit page in Visual Builder studio) is not coming. In that case, how do you customize anything in this page.