In the case you posted in picture there is a workaround. Basicly you make xsection that goes trough those patterned surfaces then you make curve out of xsection. make sketch and use project loop on that curve and later extrude it into surface. That extrude replaces merge to get one big surface.
when you change number of pattern members curve will grow and so will your extruded surface. You dont use merge here at all. This works for your example but i dont think its of any use on diffrent types of patterned surfaces.
Here is prt file:
http://www.2shared.com/file/ZA2pYT8B/prt0007prt.html
Cheers