use strict;

while(<DATA>) {
	my ($preserve) = $_ =~ /STARTPRESERVE(.*?)STOPPRESERVE/;
	s/$preserve// if $preserve;
	s/\s+/ /og;
	s/STARTPRESERVESTOPPRESERVE/$preserve/ if $preserve;
	print;
}

__DATA__
A Bridge Too Far     Hosted by Rod Stuart     Friendly Skys
42        STARTPRESERVE Life, the universe...    and      Everything     STOPPRESERVE   X-Files
HotWheels are cool     More movies on Fox           File server