The remote-exec provisioner invokes a script on a remote resource after it is created. The remote-exec provisioner supports both ssh and winrm type connections.
remote-exec connection types -
* ssh on Linux
* winrm on Windows
https://www.terraform.io/docs/provisioners/remote-exec.html

The terraform taint command manually marks a Terraform-managed resource as tainted, forcing it to be destroyed and recreated on the next apply.
This command will not modify infrastructure, but does modify the state file in order to mark a resource as tainted. Once a resource is marked as tainted, the next plan will show that the resource will be destroyed and recreated and the next apply will implement this change.
Forcing the recreation of a resource is useful when you want a certain side effect of recreation that is not visible in the attributes of a resource. For example: re-running provisioners will cause the node to be different or rebooting the machine from a base image will cause new startup scripts to run.
Note that tainting a resource for recreation may affect resources that depend on the newly tainted resource. For example, a DNS resource that uses the IP address of a server may need to be modified to reflect the potentially new IP address of a tainted server. The plan command will show this if this is the case.
https://www.terraform.io/docs/commands/taint.html

Explanation
As the instance_type is hard-coded in source module, you will not be able to change its value from destination module. Instead of hard-coding you should use variable with default values.

terraform workspace list
The command will list all existing workspaces.
Reference: https://www.terraform.io/docs/cli/commands/workspace/list.html