Run a [Code] or PowerShell script in Inno Setup compiler

You may get better answers, if you explain what you need to run the code for. Anyway...

One way is to compile the script on command-line from a batch file:

powershell -file precompile.ps1

ISCC.exe setup.iss

powershell -file postcompile.ps1

(or you can call ISCC.exe from the PowerShell script itself)

Another way to run some script before compilation is using Exec preprocessor function.

#expr Exec("precompile.bat")

or

#expr Exec("powershell -file precompile.ps1")

See also Is it possible to call a batch file while compiling an Inno Setup script?

If you need a GUI solution, there's ISTool, an Inno Setup extension, that has direct support for Pre Compilation and Post Compilation "Steps". But this project is unfortunately no longer maintained. You might be able to update it to the latest Inno Setup version, as it is open source.