About Attaching Converted Surfaces
You can select one of the following type of nodes to convert the surfaces of the selected node to a procedural surface:
A node representing one or more surfaces
Combination of sub-nodes of the same component
Combine node that contain surfaces
You can select a set of surfaces from the surfaces of a component or combine node for conversion. If the selected surface set shares a closed, two-sided edge boundary with the other surfaces of that component or combine node, the conversion tool attempts to create that two-sided boundary again so that the quilt remains closed. You may clear the Attach converted surfaces option in the Options tab before completing the conversion.
If re-attachment of the converted surface or surfaces is successful, the GTS tree changes as follows:
If you convert a surface subset of a component node that is a base-level node, active node, or nonactive sub node of a merge, a new combine node is created to take the component node’s place on the GTS tree. The original component node without the surfaces that were selected for conversion is located below the new combine node, and a new procedure node with the converted surfaces is also located below the new combined node.
If you convert one or more sub nodes of a combine node, the procedure node is created under the combine node, and this procedure node replaces all the sub nodes that you had selected for conversion.
If you convert a subset of a component sub node of a nonactive combine node, the procedure node is created directly below the existing combine node.
If re-attachment fails or you clear the Attach converted surfaces option on the Options tab, the resulting procedure node is created as a new base node, and all connections that existed with other surfaces before the surface conversion are removed. A node that is converted is removed from its previous location on the GTS tree.
If the node selected for conversion is a base node, active node, or nonactive sub node of a merge, the Attach converted surfaces option on the Options tab does not apply. In such cases, the original node is  replaced by the procedure node on the GTS tree. The one exception is if the node also contains embedded datums. In this case, a combine node that contains both the procedure node and the embedded datums replaces the original node.