Restrict updating party required of account with moves

Closes #14710

modules/account/account.py

@@ -1422,6 +1422,26 @@ class Account(
                     }),
             ]
 
+    @classmethod
+    def check_modification(cls, mode, accounts, values=None, external=False):
+        pool = Pool()
+        MoveLine = pool.get('account.move.line')
+        super().check_modification(
+            mode, accounts, values=values, external=external)
+        # Only external to allow update from template
+        if mode == 'write' and external and 'party_required' in values:
+            if to_check := [
+                    a.id for a in accounts
+                    if a.party_required != values['party_required']]:
+                if lines := MoveLine.search([
+                            ('account', 'in', to_check),
+                            ],
+                        limit=1, order=[]):
+                    line, = lines
+                    raise AccessError(gettext(
+                            'account.msg_account_party_required_with_moves',
+                            account=line.account.rec_name))
+
 
 class AccountParty(ActivePeriodMixin, ModelSQL):
     __name__ = 'account.account.party'

modules/account/message.xml

@@ -110,6 +110,9 @@ this repository contains the full copyright notices and license terms. -->
         <record model="ir.message" id="msg_account_no_type_lines">
             <field name="text">You cannot remove type of account "%(account)s" because it has move lines.</field>
         </record>
+         <record model="ir.message" id="msg_account_party_required_with_moves">
+            <field name="text">You cannot change the "Party Required" field of account "%(account)s" because it contains lines.</field>
+        </record>
 
         <record model="ir.message" id="msg_deferral_unique">
             <field name="text">Deferral must be unique by account and fiscal year.</field>