Hello,
Unfortunately the extension is not configurable; and we thought that the txt extension was the most suitable to convey our content, which is indeed text, hence should be considered safe.
Please help us understand your scenario and what kind of restriction is posed to your connection exactly.
If you prefer, you can contact us at support@lightstreamer.com
If there are more stringent conditions to be met to transport safe data, we will try to be compliant.