If you want your modified UIB file to be used as a Messenger Plus! skin, you will not need to touch any DLL file of Messenger. Refer to the
Skinning resources on details how to pack a skin for distribution. On the other hand, if you want your UIB file to be inserted into Messenger while Plus! is not installed (thus on any computer with Messenger 2009), you will have to cope with replacing the original 4010 resource in msgsres.dll, which has the number of the window (e.g. 4010 > 947 for the sign-in window) as resource name.
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