Have a will, want to do Codicil

The answer to your question depends on a number of factors. If you go back to the attorney who wrote the Will, that attorney still has the original word processor file for your existing Will, if you don't want a huge number of changes, and the Will isn't too old, then it is likely going to be more cost effective to have the attorney make whatever updates and change are needed to the Will, and then have the newly revised Willl printed out for you to execute. Doing a whole new Will also is a general best practice because it avoids the possibility for confusion, where having a Will and then one (or sometimes more than one) codicil makes it much more difficult to understand and implement the Will. But, if you can't go back to the original attorney, and if the number of changes needed is VERY small (like 1 or 2, including any corrections or updates to your existing Will that may be needed to ensure that it will still work correctly), then a codicil might be cheaper than doing a whole new Will. But if the Will is very old, if you want a lot of changes, or if it's just really poorly done, then doing a whole new Will is likely both better and more cost effective.