I don't believe you can change it, it's not user programmable on the Pro-96. In the Federal range you're talking about, it's set to 5 KHz steps.
All you can do is pick the 'side' of the one you want to listen to that sounds better. At the time the radio was made, it didn't matter, as they hadn't gone 'narrowband', and a 2.5 KHz 'error' was insignificant.
If it can be done at all, it'd have to be by something like Don Starr's programming software for the radio, which might allow entry using the internally available 6.25 and 7.5 KHz steps it uses in some spots it 'knows' had been narrowbanded.
edit - Checked Win96, and no, it' won't use anything but the 'legal' 5 KHz increments.
