What state?
Most states don't specify what the length actually is (tip to handle, actual cutting edge, etc), so it's always best to assume the worst. And by that, I mean assume that the cop that might be detaining you isn't sure what the actual legal definition is himself, and save yourself the hassle of potentially having to clear it up in court later. I'd also go a bit further than the .25", say 5/16th or 3/8" less, to be clearly under the 3" limit, and not simply at 3".
Also, if you're in a state that has cities or counties with more restrictive laws (or you travel to such cities regularly), it would behoove you to mind those laws regarding which knife you carry, and it's always a good idea to have "traveling knife". For example Chicago vs suburbs, Baltimore vs the rest of Maryland, all over the place in CA, etc.
A regrind is an option, although a "mini" version of a knife, or simply a small one that's similar might be better. A reground knife will not only require simply shortening it and putting the new tip on, but also grinding down the taper towards the tip or you'll have a thicker tip than you might want (although a "spanto" tip ala Hinderer might look cool).