Digital BW, The Print

Hi.

I just have a quick question..
The prefilled mis 3mk carts i bought from mis looks to be exactly the
same as the empty refillable carts i bought from mis for the r1800..
I have tried removing and replacing the fill plug with success..
Could this be the case? that I can refill these used carts I have? 

I could just try and see myself, but I don't know what could go wrong...

thanks,

espen