This shim was such a good idea I just had to extend its functionality. It was also a great excuse to learn more OpenSCAD...
'Tab_lgth' sets how long the tab is.
'Groovestart' defines how far from the end of the tab the base of the opening starts.
'Groove' sets the width of the opening.
'Width' sets the overall width of the shim.
'Length sets the overall length of the shim.
'Shim_thickness' still sets the shim's thickness. ;]
'Label' sets the distance of the label from the end of the tab.