I have access to an universal programmer, which can parallel program the P89C51RD2. Is it possible to reprogram the bootvector location using the parallel programming technique? Or is the chip good only for the trash can?
No P89C... is dead in a parrallel programmer regardless of boot vector and status byte.

should i parallel program the chip the first time, introducing your code for touchless ISP, and then consequently start using ISP?
That is what I do

Erik