I have a very similar question to this: Custom Fields Bulk Edit

I would like to edit ALL of the data inside a custom field but instead of replacing values I would like to instead add an attribute to the custom field on each page. Example:

This is an existing shortcode
[idx-listings linkid="387056" count="6"]
I now want to add an attribute to look like this:
[idx-listings linkid="387056" count="6" showlargerphotos="true"]
Is there a way of bulk apending the showlargerphotos attribute inside the existing shortcode without affecting the rest of the string?