Go ahead and change it. My only comment would be to consider if it is an issue of considering it two different rivers/streams or if it is still considered the same river/stream but by different names depending on location (like for example Yangtze has many local names along the way but is still considered one river). If the latter I would rather add Spangå as (alternative?) name. I think I based the relation on the names of the existing ways (I find it quite hard to understand what has happened during one individual edit here on OSM when looking at history afterwards so might be mistaken about what happened during the edit). Missing the tunnel segments was something unintentional (they are by the nature quite short and easily missed), sorry about that.