As far as I am aware, and if I am understanding what you are saying, you can't do that. I am PRETTY sure that SSDT would push across all of the solution related changes.
What I would recommend is that if Project A and Project B need to be deployed independent of each other, they should be in different solutions. At least that is how I develop software. If Project A and Project B are related but independent, then they are their own solution. If Project A relies on Project B, they are part of the same solution, but in this case, when I deploy, I deploy changes to both A and B at the same time.
An alternate approach that you could do (which is how we do it where I work currently) is to keep the SQL code out of the solution. May not be as ideal as it can be harder to find objects that use those SQL objects, but it allows you to re-use objects without needing to update every solution that uses them
The above is all just my opinion on what you should do.
As with all advice you find on a random internet forum - you shouldn't blindly follow it. Always test on a test server to see if there is negative side effects before making changes to live!
I recommend you NEVER run "random code" you found online on any system you care about UNLESS you understand and can verify the code OR you don't care if the code trashes your system.