Remove DRM legally

Hi, everybody.

We have an online music store, and we use Windows Media Right Manager 10.1 to protect and delivery licenses on our content. We have at least 150.000 tracks protected.

We protected them using sdk. We want to unprotect some tracks to delivery free and unlicensed. but we need to use the wmrm sdk to do it legally.

Does anybody know if this is possible ? i supposed that if i can protect content, i can unprotect my own content because i have the key, the header, etc.

I was reading about metadata change, or header restore. but i cant found any clue...

Thanks in advance.!

Christian