If you find word boundaries a bit hard to rely on (ie, like me, probably don't understand all the possible implications) you probably should use the more robust regex (Kenosis's 2nd example]) to dodge the bullet in some of the cases in this code (Updated to include both of Kenosis' other suggestions):

#!/usr/bin/perl
use 5.016;
use warnings;

# 1071410  change ONLY numbers which are (one digit only) 0 

my @arr = qw(20 14 007 0 1203  '' 7900130 43.02 0.03 0.0 ); 
for my $elem(@arr) { 
    if ( $elem=~ /^0{1}$/ ){ 
        say $elem;
        my $elem1 = $elem =~ s/^0{1}$/1/;
        say $elem1;
    }
}
say "above, results from Ln1-14; below: Kenosis' 3: \n";

my @arr3 = qw(20 14 007 0 1203  '' 7900130 43.02 0.03 0.0 ); 
for (@arr3) {
    print "Original \@arr3 element: |$_| becomes (or remains as) ";
    $_ = 1 if $_ == 0;
    say $_;
}

say "\n Kenosis' 1 (boundary version): ";

my @arr1 =  qw(20 14 007 0 1203  '' 7900130 43.02 0.03 0.0 ); 
for (@arr1) { 
    s/\b0\b/1/;
    print "Original \@arr1 element: |$_| becomes (or remains as) ";
    say $_;
}
[download]

Execution:

C:\> 1071410.pl
0
1
above, results from Ln1-14; below: Kenosis' 3:

Original @arr3 element: |20| becomes (or remains as) 20
Original @arr3 element: |14| becomes (or remains as) 14
Original @arr3 element: |007| becomes (or remains as) 007
Original @arr3 element: |0| becomes (or remains as) 1
Original @arr3 element: |1203| becomes (or remains as) 1203
Argument "''" isn't numeric in numeric eq (==) at 1071410.pl line 20.
Original @arr3 element: |''| becomes (or remains as) 1
Original @arr3 element: |7900130| becomes (or remains as) 7900130
Original @arr3 element: |43.02| becomes (or remains as) 43.02
Original @arr3 element: |0.03| becomes (or remains as) 0.03
Original @arr3 element: |0.0| becomes (or remains as) 1

 Kenosis' 1 (boundary version):
Original @arr1 element: |20| becomes (or remains as) 20
Original @arr1 element: |14| becomes (or remains as) 14
Original @arr1 element: |007| becomes (or remains as) 007
Original @arr1 element: |1| becomes (or remains as) 1
Original @arr1 element: |1203| becomes (or remains as) 1203
Original @arr1 element: |''| becomes (or remains as) ''
Original @arr1 element: |7900130| becomes (or remains as) 7900130
Original @arr1 element: |43.02| becomes (or remains as) 43.02
Original @arr1 element: |1.03| becomes (or remains as) 1.03
Original @arr1 element: |1.0| becomes (or remains as) 1.0
[download]

Anchoring a single zero -- as in the match and the substitution above -- seems to me the clearest way of ensuring you substitute only when the spreadsheet cells holds ONLY a single zero.

CAUTIONARY NOTE: I have not tested this with data from a spreadsheet utilizing formatted color, etc) data... and it still seems likely to fail if the column is formatted with leading zeros or a fixed number of fractional (decimalized) values (for example, if "1/2" were presented as ".50" by formatting the cell to require 2 digits after the decimal point but without requiring a leading "0" before the point).