Pre built UIAdding / Modifying field validators
Modifying the email validation function in the sign up form automatically applies the modification to the sign in form. Please refer to the Sign Up Form > Adding / Modifying field validators section.
security
Password validation in the sign in form is simply a function of if the input password's hash matches the one stored in the database for the user. As such, it doesn't make sense to apply the sign up password validation logic to the sign in form.