How to a Cassandra node see another node as down

The easiest (non-invasive) way is probably to download the tarball installation (you'll need to select either a Mac or Linux-based OS for it to allow you to download the tarball). Based-on your mention of disabling the service, I'm going to guess that you want to accomplish this on Windows. If that's not the case, please indicate so in the comments.

Un-tar dsc-cassandra-2.0.8-bin.tar.gz to the location you want to run Nodetool out of. ex:

$ cd /tools
$ tar -zxvf dsc-cassandra-2.0.8-bin.tar.gz

Note: You may have a different application you use for tarballs. I ran this from a Cygwin terminal.

Find the location of your JRE/JDK (not the bin directory) and set that as your "JAVA_HOME" (System) environment variable. When you have it set properly, you should be able to query it via CMD:

>echo %JAVA_HOME%
C:\Program Files (x86)\Java\jre7

Once you have JAVA_HOME set, it should work from either CMD or Powershell:

C:\tools\dsc-cassandra-2.0.8\bin>nodetool -h 192.168.1.85 status
Starting NodeTool
Note: Ownership information does not include topology; for complete information, specify a keyspace
Datacenter: datacenter1
========================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address       Load       Tokens  Owns    Host ID                               Rack
UN  192.168.1.85  506.29 MB  256     100.0%  cd39f0fe-ed67-40cf-b6bd-504cedabf497  rack1

This way, you can run nodetool without messing with an installer or services.

I initially just wanted to point at this as a comment, but my rep is too low. So excuse me if this is not a fully fledged answer. (Anyone feel free to edit or hint in comments)

Looking at the documentation at datastax it appears that data will be evently divided by nodes, depending on the "automagical" tokens. From my understanding it's simple as that a new vnode with new tokens just takes an even portion of each node, like all the other nodes already do. Hell, this is even what the doc says basically word by word:

Rebalancing a cluster is no longer necessary when adding or removing nodes. When a node joins the cluster, it assumes responsibility for an even portion of data from the other nodes in the cluster. If a node fails, the load is spread evenly across other nodes in the cluster.

And to address your question:

To further specify my question for virtual nodes does the cluster re-evaluate tokens for all nodes just because a new host has been added?

Sort of. The new node itself takes some partitions (evenly) from all other nodes. If you remove a node every other node will rebalance its partitions from the other nodes, making up for the lost node.