Hi Bill, if you need to extend the field to change only one attribute you can actually define the field again and only change that attribute, the ORM will keep every other attribute and change the one you re-defined. 

from odoo import models, fields

class AccountAsset(models.Model):

    _name = 'account.asset'
    _description = 'Asset/Revenue Recognition'
    _inherit = ['mail.thread', 'mail.activity.mixin']

book_value = fields.Monetary(string='Book Value', readonly=True, compute='_compute_book_value', store=True)


-- Inheritance 1: Module 1 that depends on account_asset -- 

class AccountAsset(models.Model):
    _inherit = 'account.asset' 

book_value = fields.Monetary(string='Custom string 1')

-- Inheritance 2: Module 2 that depends on module 1 (or installed after) -- 

class AccountAsset(models.Model):
    _inherit = 'account.asset' 

book_value = fields.Monetary(string='Custom string 2')

Outcome string: "Custom string 2"

It takes the last attribute defined in the AccountAsset class. ORM will automatically keep following attributes attached to the field:

• readonly=True, 
• compute='_compute_book_value', 
• store=True 

Note: other attributes might still change if they are re-defined by other modules, or they also might be shown differently in specific views, if there is some specific 'string' attribute at view-level (XML view definition).