Taskbar buttons: Never combine, TaskbarGlomLevel

Never combine:

reg add "HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced" /v TaskbarGlomLevel /t reg_dword /d 2 /f

Combine when taskbar is full:

reg add "HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced" /v TaskbarGlomLevel /t reg_dword /d 1 /f

Always combine, hide labels (default):

reg add "HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced" /v TaskbarGlomLevel /t reg_dword /d 0 /f