Well a common questions that sprouts up during customizations of MS CRM is , what are the ones which are supported , and what are the ones which should not be taken up ?
Well… the below list would throw some light on this one:
Items that supports customizations include:
Plugins to modify CRM behavior for supported Messages (create, update, delete, set state, etc.)
Modifying Navigation Items (Sitemap.xml)
Adding Buttons (ISV.config)
Creating Websites / Silverlight items to store/view from CRM
If you want a custom CRM UI look at the CRM 4.0 UII
Everything else, is unsupported , i.e.
Customizing the UI for CRM
Modifying the CRM database directly
Changing any standard CRM aspx / js / css / htc files
Whether you are working on Microsoft CRM Online (cloud) or CRM On-Premise, an unsupported customization is always an Unsupported one.
This means you won’t be able to upgrade successfully and Microsoft will not help you if you land into trouble (and probably no partners will either).
Be careful about what you want to do somethings that is unsupported !