Built-in current

Is there a way to use the "built-in current " variables (or what they are) in snippets like those that are in DB Queries e.g. ":SCHEMA_NAME" in Objects(MySQL) or ":SCHEMA_ID" in Objects(MSSQL).

No, they cannot be used in context-less code snippets, they are specific to context of executed queries for database catalog tables.

But you can use the same technique to populate the variables within code snippets, for example for T-SQL

$$
DECLARE @curr_schema SYSNAME
SET @curr_schema = SCHEMA_NAME()

SELECT ... FROM some_place WHERE SCHEMA_NAME = @curr_schema
$$

I already accomplished that. I just have to build some snippets for MySQL I had done for MSSQL in the past. I was browsing the DB queries when I spotted these and I thought if there was a shorter path I'd like to try it. Thanks, anyway.