Customize error message for trigger and display error message below the field

This Post demonstrates how to display error message in particular field level.

SObject SomeRecord;

SomeRecord.SomeField__c.addError('Custom Message');

//or

SomeRecord.someField__c.addError(someException);

Note:

We cannot add it to a field dynamically. This error mapping can only be done with a hard-coded field.

Useful Links:
https://salesforce.stackexchange.com/questions/79291/how-to-use-adderror-with-a-dynamically-derived-field-name