Is there any examples on how to modify main route table after VPC creation? Like, changing tags.

Does AWS let you modify the main route table? Or does it only let you replace it with your own route table? I believe you can use

new aws.ec2.MainRouteTableAssociation

to replace the main route table with your own (with the tags you need). If you can modify it - then you may be able to

import

the automatically created route table and then add the desired tags to it. (though this would require a multi-step deployment).