Simple request. Should be able to right click an account -> Edit Account, and have a checkbox next to "Hidden" called "Lock".

The account and all transactional data within the account would still be viewable, but no new postings would be allowed. I've used account locking frequently in my company with SAP.

Visually, perhaps the account could be greyed out? I'm thinking the VBA equivalent of .Enabled = False (using this as an example since I'm familiar with VBA).