Implement ITransactional on your section interface to enable atomic, rollback-capable updates. Mark individual properties with [IniValue(Transactional = true)] to opt them in.

[IniSection]
public interface ICredentials : IIniSection, ITransactional
{
    [IniValue(DefaultValue = "guest", Transactional = true)]
    string? Username { get; set; }

    [IniValue(DefaultValue = "", Transactional = true)]
    string? Password { get; set; }

    // Non-transactional properties are updated immediately
    [IniValue(DefaultValue = "0")]
    int LoginCount { get; set; }
}

var creds = config.GetSection<ICredentials>();

creds.Begin();          // Start transaction — old values remain visible to readers

creds.Username = "alice";
creds.Password = "secret";

if (valid)
    creds.Commit();     // Make new values visible
else
    creds.Rollback();   // Discard changes — old values restored

• Only properties that were assigned during the transaction are committed. A reload that happened between Begin() and Commit() is therefore not overwritten with the values captured by Begin().
• A committed change updates the raw value and marks the section dirty, so it is saved by the next Save() or auto-save — exactly like a normal setter.
• PropertyChanging / PropertyChanged for transactional properties are raised on Commit(), when the new value becomes visible — not by the setter during the transaction.
• Rollback() discards the pending values; no events are raised.
• A write to a key protected by a constants file throws AccessViolationException in the setter, before anything changes — also inside a transaction.

Properties without [IniValue(Transactional = true)] are updated immediately and are not affected by Begin(), Commit(), or Rollback().

• Defining-Sections — [IniValue] attribute reference
• Saving — saving transactional sections
• Reloading — effect of reload on transactional state