Grant with Grant option not working

The issue you're hitting here, is that [OMEGACA_ACC] is a server level trigger, and is not visible to [TEST], assuming [TEST] only has access to the [OMEGACA] database.

When the stored procedure [OMEGACA].[P_SYS_MANAGE_ACC] executes, it is still using [TEST]'s permissions.

You have put the "EXECUTE AS" statement as part of the trigger, meaning when it triggers, it uses [OMEGACA]'s permissions, but it does not grant other accounts ALTER permissions on the trigger.

I suggest attempting the following, though I expect it not to work:

CREATE PROCEDURE [OMEGACA].[P_SYS_MANAGE_ACC] ( 
    @p_trigger_status int
    )
WITH EXECUTE AS [OMEGACA]
AS 
BEGIN
...

My expectations are based on the following information:

• Applies only to DML statements: SELECT, INSERT, UPDATE, and DELETE.
• The owners of the calling and the called objects must be the same.
• Doesn't apply to dynamic queries inside the module

EXECUTE AS Clause (Transact-SQL) - SQL Server | Microsoft Learn

As ALTER TRIGGER is not a DML statement, that should not be sufficient.

Understanding Context Switching | Microsoft Learn has more information, and also writes the following:

Server-level impersonation can be defined in the following:

• DDL triggers

The scope of server-level impersonation is the same as that previously defined in "Explicit Server-Level Context Switching."

Database-level impersonation can be defined in the following:

• DML triggers
• Queues
• Stored procedures
• User-defined functions
• The scope of database-level impersonation is the same as that previously defined in "Explicit Database-Level Context Switching."