Of course you can, just opt out your agreement.

For example, if you are already registered with another collecting society but you want to manage In-Store with us, you will have to opt out for Background Music rights relating to the World area, excluding the United States and Canada.

If, however, you are registered with Soundreef for In-Store and want to manage royalties for online, live, mechanical rights and radio/TV with others, you can register by giving them a mandate only for those classes of rights.