If you use Notepad++ for saving text or writing programming code and wondering is there a way to replace Notepad in Windows without need to use another app such as Notepad Replacer, Notepad++ itself makes this now possible with version 7.5.9 release, the app developer has added two command line flags to Notepad++ 7.5.9 for this.
Replace Notepad with Notepad++
1. Install latest Notepad++ 7.5.9 or later on Windows.
2. Open the command prompt as administrator and run the following command
reg add "HKLMSoftwareMicrosoftWindows NTCurrentVersionImage File Execution Optionsnotepad.exe" /v "Debugger" /t REG_SZ /d ""%ProgramFiles(x86)%Notepad++notepad++.exe" -notepadStyleCmdline -z" /f
If you’ve Notepad++ 64-bit version installed, then run this
reg add "HKLMSoftwareMicrosoftWindows NTCurrentVersionImage File Execution Optionsnotepad.exe" /v "Debugger" /t REG_SZ /d ""%ProgramFiles%Notepad++notepad++.exe" -notepadStyleCmdline -z" /f

To undo the change and restore Notepad as default Text editor instead of Notepad++ in Windows, run the following command with admin privileges
reg delete "HKLMSoftwareMicrosoftWindows NTCurrentVersionImage File Execution Optionsnotepad.exe" /v "Debugger" /f
Changelog
Apart from command line flags addition that lets you replace Notepad, the Notepad++ 7.5.9 version has added a new Notepad++ Plugin API NPPM_REMOVESHORTCUTBYCMDID and the update comes included with fixes to some critical and minor bugs.
You can download latest Notepad++ from here.