Is it possible to create attachments/constraints while playing?

I want to make a train driving game and I want the player to be able to couple/de-couple from coaches or trucks. Is it possible to create constraints while playing? If not, is there an alternative?

Just you can use

Instance.new("Attachment") 

or

Instance.new("RopeConstraint")

to make them, and then set the Attachment positions, and the RopeConstraint properties.