There is a system field in the Opportunity Product entity call tax. You type the tax per item, and it sums that to form the Extended Amount.
This is pretty inconvenient and I would like modify this by changing the tax to be calculated based on the per-item price and a new field where You type in the percentage of tax on the item. I know that field can not be changed from Simple to Calculated, but if I were to make another field that to replace the current Tax field, that wouldn't work either because all of the Tax field's dependents like Extended Amount, would still be connected and calculating their values off of the Simple field Tax, not the new calculated one I created. What kind of a workaround exists?
I would've thought that I could just set it to calculate Extended Amount through my new value instead, but that won't work either. Even though it's obviously a calculated value, and it's even locked on the form, when I go into its settings, it says it's a Simple field (I'm guessing this is done for all System fields and the calculations are done behind the scenes and then inputted by the system, while You can't change it, entirely so that You can't make any changes to how its calculated), which means I can't change how the value that shows up on there is generated.
So is there any way to make a new Tax field that has the same ID or something like that, and which the rest of the application will treat as if it were the same? Or, does anyone have any ideas on other ways to fix this problem?
Have a nice day.
Create your percentage field, and then have JavasScript or a business rule that calculates the tax, and populates the standard tax field. You could hide the standard tax field as well if you'd like.