add new tasks to already assigned slots after scheduling for the first time

[AMir Firouzi]

I need some migration features for my scheduler in storm. i schedule the
tasks first time based on some logic and then after a while i need to
migrate some tasks to another workers. but after doing so if i assign the
task to an already used slot storm(nimbus) nags about not being able to use
an already used slot. is it impossible to do so? otherwise i have to use
another slots while some old used slots have the capacity to contains more
tasks and also compacting related tasks to a slot reduces intra-worker
traffic.

thanks