Way to add referencing and referenced entities of a specific entity in E-R Diagram MYSQL
SchemaCrawler is a free tool that can create database diagrams from the command-line. You can search for tables and columns that you want to include in your diagram using regular expressions. Once you have selected the tables to include, you can also include any number of levels of referenced tables in your diagram. (That is, tables related by foreign keys.) SchemaCrawler can also infer relationships even if foreign keys are not defined, if popular naming conventions are followed.

You meantion that it is tedious to manage E-R diagrams for 400 tables. Yes, it is. I would say, maintain many SchemaCrawler search expressions, which will let you generate many E-R diagrams, for example one for accounts, one for sales, and so on. The added benefit is that these diagrams never go stale - they can be regenerated instantly whenever the schema changes.

Sualeh Fatehi, SchemaCrawler