CRM 2016: How to Clear/Set Null value to a lookup which was autopopulated by an system default mapping

CRM 2016: How to Clear/Set Null value to a lookup which was auto populated by an system default mapping.

We have 2 custom(Account) lookup fields created on opportunity form. One of the lookup is Encrypted(enabled Field Level Security) which doesn't have access to all users in the system. When end users are created an opportunity from Account Entity(Sub-Grid) these custom fields are auto populated by the system default mapping, some of the users do not have access to the Encrypted field by default hence it is giving below error and not allowing to create an opportunity from Account entity only.

I am thinking issue will be resolved if we can clear or set NULL value to the Encrypted field in the system. I have tried clearing the value using JavaScript seems it is not working to the users who doesn't have permission to the Encrypted Field. Is there any way that we can impersonate and clear the value in JavaScript? Is there any approach that we can resolve the issue.

Any suggestions/comments on this would be great!

Thanks, 

Madhu M.