Your question is confusing. Are you thinking about modifying your existing ERC barrel by shortening it to 16" or re barreling to a 16" barrel with a 1:10 twist ECC barrel?
If "chopping" the existing barrel as you state, you'd better have the work done by a competent gunsmith. Any time you shorten the barrel on a gas gun, you change the pressure which could likely lead to cycling issues.
Knights rifles tend to hold their value well. Rather than modify your ECR, why don't you sell it and buy an ECC ?