why don't we insert 100', which is DH, in stead of the RA 97' ? I mean what regulation (FAR, AIM, or ICAO something, whatever ) stands for that ?
If no inner marker is installed there must be an RA minimum which you are required to use for 100' Cat II. It is not permitted to use the baralt for this minimum unless there is an inner marker. Equally, if the inner marker is installed and operational there is no general prohibition on using the baralt to fly to the DH, but as with most of these questions, whatever is in your company manual is the law for you. Sorry I don't have the time to cite the regulatory basis right now.
Edit: EASA (part SPA) "The operator shall only conduct CAT II operations if the DH is determined by means of a radio altimeter"