Different services using different port pointing to same datadir folder Let say I have already installed service MySQLa with mysqla.ini (port number=3306) setting and datadir folder in ...\data

Is it possible then, I install another service MySQLb with mysqlb.ini (port number=3307) setting and sharing datadir folder in ...\data
?

Would there be any conflict with the system schema (mysql, information_schema and performance_schema)?

I have tried locating the datadir into different folder (...\dataa and ...\datab) and it is working well.
NO!  Do not attempt to have the same files accessed by different instances of MySQL.  The code has now way of coordinating access between them.  (If it did, it would slow MySQL down to a crawl.)