Is applying kohl to the chin to strengthen hair follicles, with the aim of thickening the beard, considered haram, and does it affect the acceptance of Umrah?

It is permissible to apply kohl to a light beard to strengthen it. This does not affect someone in a state of ihram for Umrah or Hajj, because what is forbidden is dyeing the hair black, and this is a matter of scholarly disagreement. Furthermore, kohl is used for the eyes for health and adornment.