If I understand your question, it sounds like you're wanting to change variables in a Product Template interface from the Teamcenter environment without launching NX (as opposed to changing variables in a Product Template interface within the NX UI.)
Did I understand the question correctly?
In a word, this is not possible.

PTS is using the NX model update engine to make changes in template models, and this is just not available without NX running.
Ron is correct that older versions of the external Java UI for PTS could be launched into managed mode (with model open/save operations happening inside Teamcenter instead of happening on the Operating System), and that this required a bit of configuration to accomplish.
With NX 11, PTS is just part of core NX, so anytime you run NX in managed mode, PTS will also automatically follow suit.
Does that help?
Taylor Anderson
NX Product Manager, Knowledge Reuse and NX Design
Product Engineering Software
Siemens Product Lifecycle Management Software Inc.
(Phoenix, Arizona)