Pin block on streaming services I have

Sorry, that's not possible.  The individual service would have to provide that feature and I don't know if any do.  All you could do is to add a PIN to your Roku account at https://my.roku.com to prohibit channels/apps from being added and remove an app when you're finished with it and add it again whenever you want to use it.  That may be more of a pain than it's worth.  In addition, if you subscribe to any of those services through Roku you can't remove the app if you have an active subscription.