I was working with a customer who was trying to add a custom field to a CTA, and this field had a lookup to the Account object. The customer was not able to modify the field to be editable, it was and stayed a read only field. This would not work for the customers use case because this field was meant to be manually editable in order to add partner account information into the CTA. I was able to enlist the help of Wayne Baker/Gainsight TA, and we tried a few things, then he suggested we try this as a linked object instead of an account lookup. In the end, the account linked object would not work. I consulted L2 Support on this and they confirmed that this appears to be a product limitation. The customers SA Scott Drost is still investigating a possible workaround, but in the meantime I figured that it would be helpful to put this in as a product enhancement.