最初に一時ディレクトリにファイルを抽出してから、目的の場所にコピーする必要があります。このようなものが機能するはずです:
; Script generated by the Inno Setup Script Wizard.
; SEE THE DOCUMENTATION FOR DETAILS ON CREATING INNO SETUP SCRIPT FILES!
#define MyAppName "My Program"
#define MyAppVersion "1.5"
#define MyAppPublisher "My Company, Inc."
#define MyAppURL "http://www.example.com/"
#define MyAppExeName "MyProg.exe"
[Setup]
; NOTE: The value of AppId uniquely identifies this application.
; Do not use the same AppId value in installers for other applications.
; (To generate a new GUID, click Tools | Generate GUID inside the IDE.)
AppId={{5820E516-8DD7-4481-A016-63D3F00438C8}
AppName={#MyAppName}
AppVersion={#MyAppVersion}
;AppVerName={#MyAppName} {#MyAppVersion}
AppPublisher={#MyAppPublisher}
AppPublisherURL={#MyAppURL}
AppSupportURL={#MyAppURL}
AppUpdatesURL={#MyAppURL}
DefaultDirName={pf}\{#MyAppName}
DefaultGroupName={#MyAppName}
OutputBaseFilename=setup
Compression=lzma
SolidCompression=yes
[Languages]
Name: "english"; MessagesFile: "compiler:Default.isl"
[Tasks]
Name: "desktopicon"; Description: "{cm:CreateDesktopIcon}"; GroupDescription: "{cm:AdditionalIcons}"; Flags: unchecked
[Files]
Source: "C:\Program Files (x86)\Inno Setup 5\Examples\MyProg.exe"; DestDir: "{app}"; Flags: ignoreversion
; NOTE: Don't use "Flags: ignoreversion" on any shared system files
[Icons]
Name: "{group}\{#MyAppName}"; Filename: "{app}\{#MyAppExeName}"
Name: "{commondesktop}\{#MyAppName}"; Filename: "{app}\{#MyAppExeName}"; Tasks: desktopicon
[Run]
Filename: "{app}\{#MyAppExeName}"; Description: "{cm:LaunchProgram,{#StringChange(MyAppName, "&", "&&")}}"; Flags: nowait postinstall skipifsilent
[Code]
function InitializeSetup: Boolean;
var
S: AnsiString;
begin
// Show the contents of Readme.txt (non Unicode) in a message box
log('Before Extract');
ExtractTemporaryFile('myprog.exe');
log('Before FileCopy. Dest:' + ExpandConstant('{reg:HKCU\SOFTWARE\XXX,InstallPath}\file.exe'));
log('temp: ' + ExpandConstant('{tmp}\myprog.exe'));
FileCopy(ExpandConstant('{tmp}\myprog.exe'), ExpandConstant('{reg:HKCU\SOFTWARE\XXX,InstallPath}\file.exe'), false);
log('After FileCopy');
Result := True;
end;