You can change the string attribute using a custom module you may use the below code for reference:

<xpath expr="//field[@name='reference_filed']" position="attributes">
    <attribute name="string">Your String Here</attribute>
</xpath>

. You may override the field as below:

class YourModel(models.Model):
    _inherit = 'your.model'

    reference_filed = fields.FieldType(string="Your String Here")