[Белый шум]

Наверное как-то так:

var ctd[1] = document.querySelector('#shest1');
var ctd[2] = document.querySelector('#shest2');
var ctd[3] = document.querySelector('#shest3');

function next(i) {
   if( i > 3 ) return;
   if( ctd[i].checked ) {
      switch(i) {
         case 1:
            csInterface.evalScript('$._ext.evalFile("' + extensionRoot + 'b_cor_a/Minimum_Settings_A.jsx")', function() { next(i+1); });
            break;
         case 2:
            csInterface.evalScript('$._ext.evalFile("' + extensionRoot + 'add_cor_a/Skitalets_Darken_Blue_Sky_v1_1_A.jsx")', function() { next(i+1); });
            break;
         case 3:
            csInterface.evalScript('$._ext.evalFile("' + extensionRoot + 'b_cor_a/Contrast_Midtones_A.jsx")', function() { next(i+1); });
            break;
      }
   } else {
      next(i+1);
   }
}


csInterface.evalScript('$._ext.evalFile("' + extensionRoot + 'b_cor_a/Start.jsx")', function() { next(1); });