There is no set in stone rule that you have to have a take out commitment. However, without a take out commitment then your institution MAY do the permanent financing and that MAY do the permanent financing triggers the RESPA disclosures. BTW, why would you do a construction only loan if you don't have a take out commitment from another financial institution or your financial institution isn't willing to do the permanent?
Modifications do not trigger new disclosures.
The opinions expressed are mine and they are not to be taken as legal advice.