Say I want to repair Microsoft Word.

One implementation of this right is requiring Microsoft to give me access to the source code, build tooling, any engineering documents and perhaps access to the dev team depending on how far this law would go.

Another implementation, that I feel is far fairer is allowing me to interface with Microsoft Word so I could develop an alternate route to repair whatever functionality isn't working.

Microsoft already does the latter though maybe not to the level desired. They have C#, VBScript and COM. I recall using COM Interop in C# to get access to online presence data from Microsoft Lync.