You could use “ims_after_add_to_cart” or “ims_before_save_cart”,
if you use “ims_after_add_to_cart” all processing by image store is completed and saved and you will have to modify the data and save it back again to the database using “update_post_meta( $orderid, ‘_ims_order_data’, $this->cart );”
There other hooks base on specific cart actions
ims_before_save_cart_{$action}
ims_after_add_to_cart_{$action}