Fields made read only on the form will be locked in the Bulk Edit form, and form script is not executed on the bulk edit form either. If you only wanted them disabled for bulk edit you could write script to unlock those fields on the form which would execute when a user was looking at a single record. I don't think Business Rules execute on a bulk edit form, you might want to test that out if you don't want to use script to unlock the fields.
If you need it to be user specific, you would want to create multiple copies of the main form and assign the different forms (with or without locked fields) to the applicable security role.
