how big are the plants, if there still small go for if not i wouldn't recommend it because when you give roots time to grow they take off man believe me, don't want you to kill your plant.
if its not in flower do it , just be careful dig around it and try keep the rootball together with minimal soil falling off. your plant will suffer shock but it wont die.
if you flush em too first, it will reduce the stress, read riddleme's calling all newbs thread about "makin it rain" really good info!! The soil will be heavier but the plants will be sleeping