Here are some options for implementation.
1. Set up a service or application that uses the CRM web service.
- You can use a create message in .NET on some sort of a time interval based application to create an instance of the trigger entity to update the currency exchange rates.
2. Set up a workflow to trigger the creation of a trigger entity. This could be part of any workflow.
3. Just attach the plugin to any specific plugin message to trigger the update of the currencies. It is written in a message agnostic manner. Linked are all the available messages.
Again, my disclaimers are as follows:
-- This sample plugin is based on a web service provided by http://www.webservicex.net/, and I make no claims as to the reliability or validity or safety of this web service. This plugin and included solution is provided as a sample framework for how someone might design and implement a currency updater plugin based on a web service.
-- I make no claims as to the rights of use of the utilized web service (as I couldn't really find any).
--This service appears free and useful, but I make no guarantees.
--You use this plugin and project entirely at your own risk