Hi Is it possible to install LLBLGen Pro silently from the command line? Thanks

yes, use

LLBLGenPro-v540-Full-setup.exe /S

if you specify /D=path

it will override the installation path (but can't contain any quotes). It's an NSIS installer so it uses the same arguments http://nsis.sourceforge.net/nightly/Docs/Chapter4.html#silent

The VSIX installer will run though as you can't uncheck the option when using the silent installer and that install is non-silent. So it's not really supported 100% but you can get a long way.