This is my take at it:

use warnings;
use strict;

my @repls = (
    [ qr/pat1/, 'repl1' ],
    [ qr/pat2/, 'repl2' ],
    [ qr/pat3/, 'repl3' ],
);

my $txt = <<'EOF';
This is some example (pat1) text which
will be (pat3) modified according (pat2)
to some replacement (pat2) rules.
EOF

foreach my $r (@repls) {
    $txt =~ s/$r->[0]/$r->[1]/eg;
}

print $txt;
__END__
This is some example (repl1) text which
will be (repl3) modified according (repl2)
to some replacement (repl2) rules.
[download]

If you want to capture things and use them, it gets more (too?) complicated:

use warnings;
use strict;

my @repls = (
    [ qr/pat(\d+)/, 'qq{repl$1}' ],
);

my $txt = <<'EOF';
This is some example (pat42) text
EOF

foreach my $r (@repls) {
    $txt =~ s/$r->[0]/$r->[1]/eeg;
}

print $txt;
__END__
This is some example (repl42) text
[download]

Note the use of qq{} in single quotes and the double eval in the substitution. The first eval turns $r->[1] into qq{repl$1} and the second one turns that into repl42.