What type of "additional forestay" are you considering. Is it a double headstay - two forestays side by side? Or an inner forestay attached several feet aft of the stemhead?
Assuming it is the later, then there is likely no support for the
deck fitting and something will have to be added. Wotname pointed out the options for an inner forestay mast attachment - near the masthead requiring no
running backstays (often referred to as a Solent Stay) - or attached well below the masthead, with the stay parallel to the forestay, usually requiring running
backstays.
If you are considering this for an
Alberg 30, i believe there is an active owners group for that
boat. I've got to believe more than one
Alberg 30 owner has done what you are considering. I recommend you contact them.
John