Yes, you can easily replace the visual representation of nodes, without the need to recreate any nodes or reconnect any edges.
To conveniently change the visual representation of a node to another symbol, you can use the Apply and Apply Type commands from the palette's context menu.
As a first step, you need to select all nodes which you want to change. If the symbol to replace the visual representations is in a section of the palette, you can open the palette's context menu by right-clicking this symbol. From the context menu you can choose either the Apply or Apply Type command.
Use the former command to completely replace the visual representation with your symbol and the latter if you want to maintain visual aspects like, e.g. fill colors, line color, etc. from the current representation. The dimension of a selected node is maintained in either case.