You can connect as many edges to a given node as you want.
By default, new edges are connected to the center of the respective nodes. However, the connection point can be changed in several ways:
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Press and hold SHIFT while creating edges. With SHIFT down, edges start and end at the mouse position that started/ended the edge creation gesture.
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Manually adjust edge connection points. Select the edge whose connection points you want to adjust and adjust its "Source Port X", "Source Port Y","Target Port X", and "Target Port Y" properties in the properties view in yEd's lower right corner as needed.
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Run a layout or edge routing algorithm.
Manually moving a node will not change the connection points of any connected edges. Resizing a node, however, will change the connection points unless you disable "Adjust Ports on Resize" in "File" ->" Preferences", tab "Editor". Finally, some layout and edge routing algorithms also support keeping edge connection points when port constraints are specified. Port constraints can be specified using "Tools" -> "Constraints"-> "Port Constraints".