Quite surprised Farish didn't make it, except for old diecast version
Is it possible to replace chimney like Peco's Jubilee?

Not as far as I know, nobody makes a proper elliptical double chimney anyway. don't forget that not all Castles were fitted with Double chimneys, in fact only 2 out of the 8 preserved are so fitted. I have kept 2 old Farish Castles with double chimneys untill they get round to releasing a new one of the current tooling - could be a long wait!

Regards,

Alex