Hi Andrew,
Thanks for contacting us!
I just want to make sure I’m understanding your question correctly in the first instance. Taking our demo site as an example, is it the Near/Location field in the search bar that you wish to change to a dropdown?

If so, that would definitely fall into custom development territory and I’m afraid it is not something we can provide much assistance with here in the support forums (though you could certainly propose a new feature for this). On our demo site you will also see the presence of the following filter fields, including a dropdown venue filter:

This is actually a feature of Filter Bar – which is its own plugin.