WASHINGTON — The Internal Revenue Service is preparing to crack down on states that try to circumvent a new limit on the state and local tax deduction, saying on Wednesday that it will not allow local governments to find creative ways to help individuals fully deduct those taxes. The I.R.S. warning comes in response to states, like New York, that have looked for ways to blunt the impact of a new $10,000 cap on the state and local tax deduction, known as SALT. The cap, which was included in last year’s $1.5 trillion Republican tax overhaul, hit predominantly Democratic, high-tax...