First thing. The implementation of the WFFM 8.0 and later revisions were changed, so later versions were changed according to the the new functionality like storing data in the xDB analytics database and aggregating it to the SQL reporting database.
So here is what you can try to do.
Try to Override “analyticsFormsDataProvider” (the “Sitecore.WFFM.Analytics.Providers.AnalyticsFormsDataProvider” class) which is defined in the “\App_Config\Include\Sitecore.WFFM.Dependencies.config” file.
Create custom form verification action in order to change the field value before form proceeding.
If you want to know more on how to create a form verification action, You can refer to documentation:
https://sdn.sitecore.net/upload/sdn5/products/web_forms2/25/web%20forms%20for%20marketers%20v2_5%20reference-a4.pdf and look for How to Create a Form Verification Action.
So action will look like
public class CustomFormVerificationAction : BaseCheckAction
public override void Execute(ID formid, IEnumerable<ControlResult> fields)
foreach (ControlResult field in fields)
if (field.FieldName == "NewField")
string newValue = "htmlvalue";
field.Value = newvalue
In this case, your form verification action will be executed before the “Register a Goal” system action and the changed field value will be saved to xDB.
Try and see if this gives enough direction and works for you.