I am wondering if it’s possible to retrieve the value (‘123456’) associated with the parameter in a URL (e.g. in “&code=123456”) and use it with an ‘If’ logic to display something if the value matches the user meta.
I wasn’t sure if the URL query feature simply retrieves the query parameter and not the value.
Use the query attribute to get a parameter value by referencing its name:
<Url query=color />
So in your case if your URL is mysite.com/?code=123456 you could get the value with <Url query=code />. If you wanted to pass that to the If tag, it might look something like this:
<If check="{Url query=code}" is value="{User custom_field_name}">
The URL parameter matches your user field.
</If>
or maybe
<If user_field="custom_field_name" is value="{Url query=code}">
The URL parameter matches your user field.
</If>