Once you have mastered code replacements, you can combine multiple code replacements with variables to save time. In this example, you have a team of 4 photographers covering a music festival with 4 stages over a few days, and you want to download all their photos from different days into a single contact sheet. 

You could caption all those by hand, but setting up a code replacement file using multiple variables can speed things up exponentially. You could differentiate the images from each photographer by using the serial number of their camera since this is a unique variable that is already stored with each photo. 

This example code replacement file lists the serial number of each camera along with the name of each photographer, which stage they are covering, and the name of the performing artist, all separated with tabs, along with a simple single code replacement for the name of the music festival. 

51115555111555       Jimmy Bits         Montana Stage        Davide Crowie
13000000000031 Jane Lensy Utah Stage Motley Brew
12341234123412 Rita Reflex Colorado Stage Taylor Sleaux
78978978978978 Phil Filter Texas Sage Red Hot Eggplants
bmf Big Music Festival presented by Trustworthy Motors

(The actual code replacement file should use tabs between fields and not spaces.)

Even though there are photos from different photographers shooting different subjects in different locations on different dates, you can use the Metadata (IPTC) Template to batch apply a single caption in the IPTC Caption field for all photos from that shoot:

={serialnum}#3= performs on the  ={serialnum}#2= at the =bmf= on {monthname3} {day}, {year4}. Photo by staff photographer ={serialnum}#1=

For Jimmy, the replacements would make the captions read:

David Crowie performs on the Montana Stage at the Big Music Festival presented by Trustworthy Motors on Jan 6, 2013. Photo by staff photographer Jimmy Bits

While Rita's would read like this:

Taylor Sleaux performs on the Colorado Stage at the Big Music Festival presented by Trustworthy Motors on Jan 4, 2013. Photo by staff photographer Rita Reflex
That also means that if you have any last-minute changes in sponsorship, you can simply change the text in the code replacement file.

More Code Replacement Ideas

Code replacement can be used in any of the fields of the Metadata (IPTC) Template. This means it can help speed up keywording. For example, if you are a wedding photographer who archives files with keywords to be able to find them later, you could set up a code replacement file that covers your common keyword fields

familyname       Davis
groomname     Dave Davis
bridename     Jane Jensen
motherofbride    Dorothy
motherofgroom    Diane
bestman         Bert Baker
maidofhonor     Betsy Bouffant

Then you could keep a saved Metadata (IPTC) Template that you plan to reuse with keyword field that contains items like \familyname\ and \maidofhonor\ etc. You could then keep the same Metadata (IPTC) Template and just edit your code replacement file before or after each shoot to match the members of that wedding.

Note: To make this work, you would create a Metadata Template with delineated Core Replacements before loading a specific code replacement file and before setting a default replacement in the "Code Replacements" dialog so that the code replacements do not get immediately evaluated when you are trying to create the template. Once you have created and saved your templates, you can then set a default replacement in the "Code Replacements" dialog.

You can also use code replacement to adjust the way Variables work. For example, using the {lt} variable for "lens type" will insert something like "EF24-105mm f/4L IS USM" If you prefer a shorter description for that variable, you could set up code replacement file with this line:

EF24-105mm f/4L IS USM    24-105mm f/4L IS

and then use \{lt}\ in your Stationery Pad to insert the new shorter value. And since you can load multiple code replacement files, you can keep this one in the list all the time even as you swap out other code replacement files.