Author: Kevin Gallagher 

How do you change the primary mouse button

Answer:

To change the primary mouse button in code you need to execute an API function 
called SwapMouseButton. This changes the primary button but does not alert the 
control panel applet for the mouse that the primary button has changed. To do this 
we need to write to the registry. The code below shows how to toggle the primary 
mouse button by first reading the registry to determine the current assignment then 
does the toggle by writing to the registry and executing the SwapMouseButton 
function. 

1   uses Windows, Registry;
2   
3   const
4     LeftButton = '0';
5     RightButton = '1';
6     VaueToRead = 'SwapMouseButtons';
7   begin
8     with TRegistry.Create do
9     begin
10      try
11        if OpenKey('Control Panel\Mouse', False) then
12        begin
13          if ValueExists(VaueToRead) then
14            if ReadString(VaueToRead) = LeftButton then
15            begin
16              SwapMouseButton(True);
17              WriteString(VaueToRead, RightButton);
18            end
19            else
20            begin
21              SwapMouseButton(False);
22              WriteString(VaueToRead, LeftButton);
23            end;
24          CloseKey;
25        end;
26      finally
27        Free;
28      end;
29    end;
30  end.