I agree with tyhjaarpa.
A speaker's sensitivity is a complex result of the individual drivers' sensitivity, the cabinet size & tuning, and the crossover. The cabinet size & tuning affects the sensitivity of the woofer(s) in the lower and mid bass range.
The crossover affects the sensitivity within one octave (for a 4th order crossover) or two octaves (for a 2nd order) of the crossover frequency.
The cabinet size & tuning probably has a larger effect on a speaker's overall sensitivity.
I want to change the drivers in my center channel speaker to make it more efficient. The sensitivity of the speaker is 88db. If I swap the drivers out to lets say 94db. would the speakers have a sensitivity of 94db? or would I also have to change the speakers crossover?
If you swap out the drivers (which ones?) you would almost certainly have to build a new cabinet of different dimensions, and redesign the crossover.
If your center channel speaker truly has a sensitivity of 88 dB, it should be fine as is. Are there other problems you have with it?
Drivers and finished speakers with an honest 94 dB are very rare, and are usually better suited for large auditoriums or outdoor use. Speaker makers often exaggerate sensitivity numbers as they know customers attach too much importance to higher values.