$_ = "I like the number 4 and I left my dog in the garage last night on accident"; # which I did...poor pup :-/

# store "number xx" where xx is a natural number as a 
# backreference and replace it with itself followed by
# 
s/(?>number \d+)/ as well as the number 7/g;

print $_,$/;

__DATA__
output:
I like the number 4 as well as the number 7 and I left my dog in the garage last night