It is not possible to set an effect name that is longer than 39 bytes via scripting

The bug is that the effect name cannot be set via scripting if the name is more than 39 bytes. Adobe bug ID: DVAAE-4229694

You can use the effect index instead of its name using a function like this:

function getEffectIndex(layer, effectName) {
  for (var i = 1; i <= layer.effect.numProperties; i++) {
    if (layer.effect(i).name == effectName) {
      return i
    }
  }
  return null
}

// usage
var proj = app.project;
var thisComp = proj.activeItem;
var layer = thisComp.layer(1);

layer.effect(getEffectIndex(layer, 'longEffectName'))(1).setValue(100)