I haven't seen the circuit for that design, but be aware that ICSP requires that the PGC, PGD & MCLR pins of the PIC be usable for that purpose.
In other words, the circuit must be designed to allow ICSP. It's not just a header tacked on as an afterthought.
In other words, the circuit must be designed to allow ICSP. It's not just a header tacked on as an afterthought.