It's great that so much feedback comes together.

An advertised advantage of Atelier is the SCM functionality. How does this look like with VSCode? Is there a manual or examples? Are there differences between VSCode and Atelier?

Unfortunately, we have no experience with this yet. 

Ok, quick and dirty, try this

s stream=##class(%FileBinaryStream).%New()
s stream.Filename = filename
s propertyPath = "PIDgrpgrp(1).ORCgrp(1).OBXgrp(1).OBX:5(1)"
s seg=target.GetMutableSegmentAt($P(propertyPath,":",1),.tSC)
s tSC = seg.StoreFieldStreamBase64(.stream,$P(propertyPath,":",2),,0)

set tSegString=""
    set tSegStringCleared="" 
    set tSegString = target.GetValueAt("PIDgrpgrp(1).ORCgrp(1).OBXgrp(1).OBX:5(1)")
    set tSegStringCleared = $translate(tSegString,$c(13,10))
    set tSC = target.SetValueAt(tSegStringCleared,"target.{PIDgrpgrp(1).ORCgrp(1).OBXgrp(1).OBX:5(1)}","set")

I'll ask again so I understand you correctly. 

You want to have another OBX segment with each CRLF or another OBX:5(*) field?
More segments would create too much overhead. 
I think the IHE Radiology Profile recommends a new segment every 62k bit.

With repeated fields in OBX:5 it's not HL7 standard conform.

Or would you like an OBX:5 field with the value ABCDEFGHIJKL...