Handling and customizing errors and messages in Inno Setup - inno-setup

Question

Inno Setup will show different message boxes to the user.
For example,
When it tries to install a file that is in use, it will show a message to abort/ignore/cancel.
When the setup is installing the files and the target path will have low space while installing, the setup will give an error.
I need to customize these message boxes on my own. (I do not want these native messages to be shown to the user) for example, I need to show another message box, or even totally do not show a specific message from Inno Setup, or changing a label when that message is going to fire.

Answer 1

All Inno Setup messages can be customized using the [Messages] section.
Some examples:
How to modify error message in Inno Setup?
Show a custom message for unsupported architectures
How can I show my own message and then exit setup if the current version of Windows is not supported?
As for the change of the message box layout/design. You cannot really change it. With some fancy implementation of Check and BeforeInstall parameters, you might be able to catch some problems before Inno Setup detects them and handle them your custom way. But that's lot of work with unreliable results.
If you tell us what are you trying to achieve more specifically, you may get more specific answer.
If you need a solution that allows everything that Inno Setup allows on error, including clean abort of the installation, Check or BeforeInstall won't help as they do not have a way to cleanly abort it.
You would have to do all the checks before the installation, e.g. in CurStepChanged(ssInstall).
[Files]
Source: "MyProg.exe"; DestDir: "{app}"; Check: ShouldInstallFile
[Code]
var
DontInstallFile: Boolean;
function ShouldInstallFile: Boolean;
begin
Result := not DontInstallFile;
end;
procedure CurStepChanged(CurStep: TSetupStep);
var
FileName: string;
Msg: string;
Response: Integer;
begin
if CurStep = ssInstall then
begin
FileName := ExpandConstant('{app}\MyProg.exe');
repeat
if FileExists(FileName) and (not DeleteFile(FileName)) then
begin
Msg := Format('File %s cannot be replaced', [FileName]);
Response := MsgBox(Msg, mbError, MB_ABORTRETRYIGNORE)
case Response of
IDABORT: Abort;
IDIGNORE: DontInstallFile := True;
end;
end;
until (Response <> IDRETRY);
end;
end;