You can configure the ptc.opt file in the FlexNet folder to allow only you to use a certain license.
If the new ISDX license is floating, you can do it in the *.psf file by have a dedicated *.psf for you which has the module enabled and the rest of your users have a different *.psf file.
The ptc.opt settings are in the FlexNet User guide, but I don't think PTC has implemented all of the options. You can download a copy from PTC.com.
Thank you,
Ben H. Loosli
USEC, INC.