A Frensi rig doesn't require any permanent changes to your Laser (or ILCA).
Most of the Laser dinghy parts, the dagger board and rudder, the lower mast, the mainsheet, are used for the Frensi too. The only Laser parts you don't use with the Frensi are the boom and the top mast.
The Frensi rig comes with two booms and a short top mast. The lower boom is joined at the front end to the upper boom by a shackle.
The short top mast is called a "halyard mount". It pushes into the top end of the lower mast in exactly the same way as the Laser top mast does.
The halyard mount has the pulley and cleat on it for the halyard rope. The halyard mount attaches to the upper boom by the halyard rope used to raise and lower the rig/sail. There is a metal eye on the upper boom that is used for the halyard rope.