Examples based on latest version:
37mm Anti-tank Guns in 41 Panzer Division, 41 Elite Motorized Regiment, 41 SS Motorized Division (-), 41b SS Motorized Division, 41 Motorized Division, 41 Motorized Brigade, 41 Mountain Division, 41 Security Division, 41 SS Infantry Division, 41 AC Sturm Division, 41c Infantry Division, 41 Flieger Division, 41 Airlanding Division, 41 Jager Division will rely on swap
Panzerjager I in 41 SS Motorized Division, 41 Motorized Brigade will rely on swap
50mm Anti-tank Gun, 41 Jager Division in 41 Airlanding Division will rely on swap
Motorized Rifle Squad in 41 SS Motorized Brigade
Rifle Squad and 7.92mm Anti-tank Rifle in 41 Fortified Zone will rely on swap
Rifle Squad, Pioneer Squad, 50mm Anti-tank Gun, Marder II, sIG33 in 42 SS Cavalry Division will rely on swap
This is very common, so it should work as smooth as upgrade procedure, not as an emergency. Swap is required every time where the element is no longer available to be built when given TOE is active (or ceases to be available during TOE active life).
Just look at my TOE Details report and look for items marked with "#-+". Will soon upload files based on latest beta.