First Remove the Automatic ID from front end – Property Page with this CSS.

#propertyid_display{   
display:none;   
} 

To add a new custom field for property custom ID go to General – Custom fields:

 

This is an example to add the manual ID as numeric field type

manualid

Then you can add this field in advanced search:

 

The field should be set as in below screenshot if it’s a numeric field.

manualid2

 

This ID can be added in Admin when adding/editing property or in Front End submission form when submitting property.

To learn more on what kind of fields you can add in Advanced Search custom setup please go here – http://help.wpresidence.net/article/adv-search-custom-fields-setup/