You may have no choice dependent on insurer, but do be aware that although many mainstream insurers will insure you with mods, they will not cover the cost of replacement should the worst happen. For example, Admiral group will let you put a nice set of wheels on, but if you find a wall jumping out at you one day then they'll only replace them with stock wheels. Unless you pay their extra premium of course...
Always worth asking whether the value of the mods is insured, and it might be worth paying more to ensure they are.