Adding a new switch with an independent light in an existing circuit - With photos
Whether you can simply break that light off the circuit and put it on a new switch depends completely on how the power is run.

If the light is fed in the ceiling, then yes you can just add a new switch.
Existing wiring:


With the new switch:




However if the power comes through the existing switch then no you will have to run a new feed to the light. That feed can go through the new switch (shown in the bottom diagram), or straight to the light whichever is easier.
Existing wiring:


The new diagram for this scenario:


Who said MS paint couldn't be used for wiring diagrams...