I am no expert, but if you have no boom... and shorten the sail by removing bottom panels... your mainblocks... traveler will have different angles and you will need to have allot more main sheet to handle the extra space. If it is a foot higher and you have an 8-1 block.. you will need 8 feet more sheet.

another consideration is the hook on top. If you have a hook and ring system (and you wish to lower the top of the sail down) you will have to either flip the boat to take the ring off... or come up with some way of twisting the ring for lowering the sail. Perhaps a small line tied to the bottom of the ring....