Yes you can reuse them but you need to be careful as to what circuitry you hang off the pins.

Most ICSP programmers have 4.7K pull-down resistors on the PGC/PGD pins and assume the pins will idle low.
You shouldn't put too much additional load on the pins, add pullups or capacitors, or use the pins as inputs if they'll be actively driven high/low by the connected circuitry.