AFAIK it's not possible to rewrite the bootloader memory internally. But if anybody wants to try out the new Optiboot v4.4 and they have two Arduino boards, the Optifix sketch avoids the need to disable auto-reset on the board acting as programmer. Once one of the boards has Optiboot v4.4 installed it will run ArduinoISP properly (again without fiddling about disabling the reset signals). Although for this purpose IMHO Optifix is easier to use than ArduinoISP + AVRdude.
I hope WestfW doesn't mind me beating this particular drum. It's all his work.