The below can be used to perform any action on a field value change.
Global
Triggers: onAfterUserUpdate
User: Automatic
Access: Everybody
Conditions
Field: Custom > Value
Custom Value: [var1_FIELD_NAME]
Operator: Not Equal To
Value: [var3_FIELD_NAME]
Replace FIELD_NAME with the name of the field you want to condition against. Next lets combine this with a Code action to disable their account in the below example.
Global
Triggers: onAfterUserUpdate
Type: Code
User: Automatic
Access: Everybody
Conditions
Field: Custom > Value
Custom Value: [var1_cb_address]
Operator: Not Equal To
Value: [var3_cb_address]
Action
Method: PHP
Code:
$user->set( 'block', 1 );
$user->set( 'approved', 0 );
$user->store();
The above example should block their account and mark it pending moderator approval if the cb_address field is changed.