No, it's not possible to downgrade to an unsigned version of iOS as part of the installation procedure is an online verification with the Apple update servers, which will cause the installation to fail every time.
The current software is 10.2. If you try reverting to iOS 10.2 when Apple is signing a different software, it will not work. During the installation process, iTunes connects to Apple's servers to make sure you don't install software not signed by them. You'll get error 3194, and it will not be possible to proceed. So: no, you can't use your blobs to go back to 10.2 once it's not signed any more.
If you really want an iPhone running iOS 9.3.5 you'll have to buy a used one that was never upgraded to iOS 10.