The replace command is a very simple but VERY powerful command that comes as part of mysql. It can be used to quickly replace entries within a group of files. Generally I find it useful for mass-modification of an IP for dns or TTL for dns.

The general format:
replace a b b a -- file1 file2

In english:

replace 14400 3600 -- /var/named/*db*

Where 14400 is the old term and 3600 is the term you want to replace it with. The *db* just means it does it to any file with db in the name in the /var/named/ directory.