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.
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The opinions expressed are mine and they are not to be taken as legal advice.