How can I trigger a rules event by code ? I'm using Commerce for the website I'm building right now.
I want to trigger the event "Calculate the sell price" after an order is updated to a status, I made one called "Approved". 
The reason I want to do that is that the Tax is calculated at this event and at the "Checkout: Checkout" page, but the store manager wants to choose if the customer should pay tax or not, he wants to do that manually not using billing or shipping conditions.

I added a boolean field "Apply VAT?" to  the order page and added a condition if that entity exists and is true to apply the VAT tax, but this is:not done at the checkout page and I noticed that if I change the status back to "Checkout: Checkout" the VAT tax is applied and this is because of the "Calculate the sell price" event (tell me if I'm wrong).

I was thinking to build a rule with the event "Order is updated" and the action to be a PHP code to invoke the event again, I know about rules_invoke_event, but I can't get it working.

I also have problems with the tax not being applied to the shipping cost, but this is another problem (maybe I will open another question of this)

I will appreciate any answers, thanks!
I managed to invoke the event "calculate sell price" by adding a rule with the event "When existin line item is updated" and then adding a call to rules_invoke_event() in PHP code like this:

rules_invoke_event("commerce_product_calculate_sell_price", $commerce_line_item);


I was previously calling this rule incorrectly, without adding the $commerce_line_item so this problem is resolved, now the shipping remained.
Thanks for your time!