How to do rail spacing correction to satisfy insurance carrier

[Penny Clark]

Hi All,

Since we had to secure a liability only policy for our mountain vacation rental, they told us we needed to correct the rail spacing and had only a certain time to do it. The posts are 5 inch apart and must be corrected to 4 inch. Are there any DIYers out there who have done this using the existing rails and reducing the space between by inserting metal rails? Or would it be better to lay down new rails with spindles, assuming we can use the existing posts? 

Any advice would be appreciated!