See comments.

foreach my $line (@vcvars) {
    if ($line =~ /^set INCLUDE=(.*)/) { ## use the ^ and $ anchors whe
+never possible
        my @paths = split(/;/, $1); # $1 is the part in brackets in th
+e regex above
        print VCVARS32 "set INCLUDE=";
        print VCVARS32 join(";",  # concatenate list of strings using 
+semicolons
            grep( !/^\%SRVBUILD\%/, @paths) # return list of the strin
+gs that do not start with %SRVBUILD%
        );
        print VCVARS32 "\n";
        next;
    }
    # no else{} necessary; next() will prevent you falling through to 
+here

    # in you "set SRVBUILD" case:
    # $line =~ s/^\=(\W*)/\=/;
    # this will not work since you're using an ^ anchor;
    # the "=" is not at the beginning of the string, is it?
    # also, \W matches any NONword-character; anything NOT a letter, d
+igit or underscore
    # but if I understood correctly you want to change everything afte
+r the "="

    # you can simply use a s///ubstitution here
    # since if the left side does not match, nothing gets replaced;
    # no need for an if(){}
    s/^(set SRVBUILD)=.*/$1=INI_CODE_HERE/;

    # and then we can just let the boilerplate print handle the modifi
+ed $line
    print VCVARS32 $line; 
}
[download]

____________
Makeshifts last the longest.