Just use blind rivets and drill them out when you need to replace a part or use stainless steel screws (parkers). The latter are surprisingly strong and the little corroding that does happen between the stainless steel screw and the alu beam prevents further corrosion and locks the screw tightly in place.

Have used the screw option on my spi halyard cleat on my mainbeam. I'm pushing 5 seasons now and no troubles with either loads or corrosion.

Wouter