https redirection with URI Masking

if {[HTTP::host] eq "abc.com"} {
  if {[HTTP::uri] eq "/"} {
    HTTP::uri "/abc/"
  }
}

The rewriting of the URI should in no way affect the content that is returned by the webserver. As long as the same content is in /abc/ then it should work fine. You may need to check your webserver configuration to ensure certain filetypes (php etc) will be recognised in the new directory because of possible security restrictions.