There is no black and white answer to that question.

Some very simple programs may work (all security vectors will be blocked), others appear to work fine but seem to be missing some features (Repelit blocked some security vector entries), but the majority of installations will not work. 

Plug-n-play devices will work without changing into an install mode. 

Remember Repelit is designed to prevent unwarranted and internet drive-by installations.  When you switch to an install mode you are approving an install with Repelit and receiving on-guard installation protection.

A simple rule of thumb is, “when doing an installation first switch to an install mode.”