freeze plug weeeeping

Hi there,
I have an 850 mini (a series BMC engine), and I have a leaky freeze plug.
can I replace this while the engine is in the car?
any experience out there oh wise ones?

the freeze plug is the one right in front as you look at the engine, right 
by the dipstick. It is weeping in the center (looks like corrosion or 
galvanic reaction has caused it because it is not along the mating surfaces, 
but right smack dab in the center)...thanks in advance!!