How you can remove a snap constraint?
To remove a snap constraint, the geometry needs to be moved in some way. For example, an intersection snap could be overruled by defining a new length constraint that pushes past the snap.
One general way could also be : create a new element, like a line, snapping on the point you want to remove the snap constraint from. Then move the point of the civil geometry to snap onto this element. Then delete the element.