Assuming you are managing the contents of the barcode field (to prevent duplicates or null values for example) you can do something like this via an Automated Action that runs on create and update of the Product Template:

product_barcode = record.barcode
env.cr.execute("SELECT * FROM ir_model_data WHERE module=%s and name=%s",                       
              ("barcode", product_barcode))
if env.cr.rowcount == 0:  
    env.cr.execute(""" INSERT INTO ir_model_data (module, name, model, res_id, date_init, date_update)                               
           VALUES (%s, %s, %s, %s, (now() at time zone 'UTC'), (now() at time zone 'UTC')) """, 
                  ("barcode", product_barcode, "product.template", record.id))

Note that this is the same way Odoo checks for and assigns External ID's during the import process:

\https://github.com/odoo/odoo/blob/11.0/odoo/addons/base/ir/ir_model.py#L257

XML ID UPDATE