Change Wix Merge Module Package GUID?

When is it necessary to change the package GUID of a merge module?

<Wix xmlns="http://schemas.microsoft开发者_如何学Go.com/wix/2006/wi">
 <Module Id="MyMergeModule" Language="1003" Version="1.0.0.0">
  <Package Id="SOME_GUID" Manufacturer="Me" InstallerVersion="301" />
 </Module>
</Wix>

Wix3 requires that the package GUID is explicitly specified for a merge module unlike for a product. My merge module will be used with an MSI that is built bi-weekly. These bi-weekly MSIs need to co-exist on the same machine as separate installations (e.g. versions 1, 2, 3, etc...) Do I need to change the package GUID of my merge module for each bi-weekly MSI build?

The installer that consumes the merge module will have to have a new ProductCode/PackageCode every other week, a different isolated destination directory and not implement a MajorUpgrade. The ModuleSignature doesn't need to change as each installed product can deploy the same component id's to different locations.

In WiX v3.0+ it's best to leave the Package/@Id absent all the time and let the toolset handle it for you. In WiX v2.0 it's best to to use the all ? GUID to ensure a new GUID is creaed for you.