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.